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Sourcecode: postgresql-8.4 version File versions

heapam.c

/*-------------------------------------------------------------------------
 *
 * heapam.c
 *      heap access method code
 *
 * Portions Copyright (c) 1996-2009, PostgreSQL Global Development Group
 * Portions Copyright (c) 1994, Regents of the University of California
 *
 *
 * IDENTIFICATION
 *      $PostgreSQL: pgsql/src/backend/access/heap/heapam.c,v 1.277 2009/06/11 14:48:53 momjian Exp $
 *
 *
 * INTERFACE ROUTINES
 *          relation_open     - open any relation by relation OID
 *          relation_openrv - open any relation specified by a RangeVar
 *          relation_close    - close any relation
 *          heap_open         - open a heap relation by relation OID
 *          heap_openrv       - open a heap relation specified by a RangeVar
 *          heap_close        - (now just a macro for relation_close)
 *          heap_beginscan    - begin relation scan
 *          heap_rescan       - restart a relation scan
 *          heap_endscan      - end relation scan
 *          heap_getnext      - retrieve next tuple in scan
 *          heap_fetch        - retrieve tuple with given tid
 *          heap_insert       - insert tuple into a relation
 *          heap_delete       - delete a tuple from a relation
 *          heap_update       - replace a tuple in a relation with another tuple
 *          heap_markpos      - mark scan position
 *          heap_restrpos     - restore position to marked location
 *          heap_sync         - sync heap, for when no WAL has been written
 *
 * NOTES
 *      This file contains the heap_ routines which implement
 *      the POSTGRES heap access method used for all POSTGRES
 *      relations.
 *
 *-------------------------------------------------------------------------
 */
#include "postgres.h"

#include "access/heapam.h"
#include "access/hio.h"
#include "access/multixact.h"
#include "access/relscan.h"
#include "access/sysattr.h"
#include "access/transam.h"
#include "access/tuptoaster.h"
#include "access/valid.h"
#include "access/visibilitymap.h"
#include "access/xact.h"
#include "access/xlogutils.h"
#include "catalog/catalog.h"
#include "catalog/namespace.h"
#include "miscadmin.h"
#include "pgstat.h"
#include "storage/bufmgr.h"
#include "storage/freespace.h"
#include "storage/lmgr.h"
#include "storage/procarray.h"
#include "storage/smgr.h"
#include "utils/datum.h"
#include "utils/inval.h"
#include "utils/lsyscache.h"
#include "utils/relcache.h"
#include "utils/snapmgr.h"
#include "utils/syscache.h"
#include "utils/tqual.h"


/* GUC variable */
bool        synchronize_seqscans = true;


static HeapScanDesc heap_beginscan_internal(Relation relation,
                                    Snapshot snapshot,
                                    int nkeys, ScanKey key,
                                    bool allow_strat, bool allow_sync,
                                    bool is_bitmapscan);
static XLogRecPtr log_heap_update(Relation reln, Buffer oldbuf,
               ItemPointerData from, Buffer newbuf, HeapTuple newtup, bool move);
static bool HeapSatisfiesHOTUpdate(Relation relation, Bitmapset *hot_attrs,
                                 HeapTuple oldtup, HeapTuple newtup);


/* ----------------------------------------------------------------
 *                                   heap support routines
 * ----------------------------------------------------------------
 */

/* ----------------
 *          initscan - scan code common to heap_beginscan and heap_rescan
 * ----------------
 */
static void
initscan(HeapScanDesc scan, ScanKey key, bool is_rescan)
{
      bool        allow_strat;
      bool        allow_sync;

      /*
       * Determine the number of blocks we have to scan.
       *
       * It is sufficient to do this once at scan start, since any tuples added
       * while the scan is in progress will be invisible to my snapshot anyway.
       * (That is not true when using a non-MVCC snapshot.  However, we couldn't
       * guarantee to return tuples added after scan start anyway, since they
       * might go into pages we already scanned.      To guarantee consistent
       * results for a non-MVCC snapshot, the caller must hold some higher-level
       * lock that ensures the interesting tuple(s) won't change.)
       */
      scan->rs_nblocks = RelationGetNumberOfBlocks(scan->rs_rd);

      /*
       * If the table is large relative to NBuffers, use a bulk-read access
       * strategy and enable synchronized scanning (see syncscan.c).    Although
       * the thresholds for these features could be different, we make them the
       * same so that there are only two behaviors to tune rather than four.
       * (However, some callers need to be able to disable one or both of these
       * behaviors, independently of the size of the table; also there is a GUC
       * variable that can disable synchronized scanning.)
       *
       * During a rescan, don't make a new strategy object if we don't have to.
       */
      if (!scan->rs_rd->rd_istemp &&
            scan->rs_nblocks > NBuffers / 4)
      {
            allow_strat = scan->rs_allow_strat;
            allow_sync = scan->rs_allow_sync;
      }
      else
            allow_strat = allow_sync = false;

      if (allow_strat)
      {
            if (scan->rs_strategy == NULL)
                  scan->rs_strategy = GetAccessStrategy(BAS_BULKREAD);
      }
      else
      {
            if (scan->rs_strategy != NULL)
                  FreeAccessStrategy(scan->rs_strategy);
            scan->rs_strategy = NULL;
      }

      if (is_rescan)
      {
            /*
             * If rescan, keep the previous startblock setting so that rewinding a
             * cursor doesn't generate surprising results.  Reset the syncscan
             * setting, though.
             */
            scan->rs_syncscan = (allow_sync && synchronize_seqscans);
      }
      else if (allow_sync && synchronize_seqscans)
      {
            scan->rs_syncscan = true;
            scan->rs_startblock = ss_get_location(scan->rs_rd, scan->rs_nblocks);
      }
      else
      {
            scan->rs_syncscan = false;
            scan->rs_startblock = 0;
      }

      scan->rs_inited = false;
      scan->rs_ctup.t_data = NULL;
      ItemPointerSetInvalid(&scan->rs_ctup.t_self);
      scan->rs_cbuf = InvalidBuffer;
      scan->rs_cblock = InvalidBlockNumber;

      /* we don't have a marked position... */
      ItemPointerSetInvalid(&(scan->rs_mctid));

      /* page-at-a-time fields are always invalid when not rs_inited */

      /*
       * copy the scan key, if appropriate
       */
      if (key != NULL)
            memcpy(scan->rs_key, key, scan->rs_nkeys * sizeof(ScanKeyData));

      /*
       * Currently, we don't have a stats counter for bitmap heap scans (but the
       * underlying bitmap index scans will be counted).
       */
      if (!scan->rs_bitmapscan)
            pgstat_count_heap_scan(scan->rs_rd);
}

/*
 * heapgetpage - subroutine for heapgettup()
 *
 * This routine reads and pins the specified page of the relation.
 * In page-at-a-time mode it performs additional work, namely determining
 * which tuples on the page are visible.
 */
static void
heapgetpage(HeapScanDesc scan, BlockNumber page)
{
      Buffer            buffer;
      Snapshot    snapshot;
      Page        dp;
      int               lines;
      int               ntup;
      OffsetNumber lineoff;
      ItemId            lpp;
      bool        all_visible;

      Assert(page < scan->rs_nblocks);

      /* release previous scan buffer, if any */
      if (BufferIsValid(scan->rs_cbuf))
      {
            ReleaseBuffer(scan->rs_cbuf);
            scan->rs_cbuf = InvalidBuffer;
      }

      /* read page using selected strategy */
      scan->rs_cbuf = ReadBufferExtended(scan->rs_rd, MAIN_FORKNUM, page,
                                                         RBM_NORMAL, scan->rs_strategy);
      scan->rs_cblock = page;

      if (!scan->rs_pageatatime)
            return;

      buffer = scan->rs_cbuf;
      snapshot = scan->rs_snapshot;

      /*
       * Prune and repair fragmentation for the whole page, if possible.
       */
      Assert(TransactionIdIsValid(RecentGlobalXmin));
      heap_page_prune_opt(scan->rs_rd, buffer, RecentGlobalXmin);

      /*
       * We must hold share lock on the buffer content while examining tuple
       * visibility.    Afterwards, however, the tuples we have found to be
       * visible are guaranteed good as long as we hold the buffer pin.
       */
      LockBuffer(buffer, BUFFER_LOCK_SHARE);

      dp = (Page) BufferGetPage(buffer);
      lines = PageGetMaxOffsetNumber(dp);
      ntup = 0;

      /*
       * If the all-visible flag indicates that all tuples on the page are
       * visible to everyone, we can skip the per-tuple visibility tests.
       */
      all_visible = PageIsAllVisible(dp);

      for (lineoff = FirstOffsetNumber, lpp = PageGetItemId(dp, lineoff);
             lineoff <= lines;
             lineoff++, lpp++)
      {
            if (ItemIdIsNormal(lpp))
            {
                  bool        valid;

                  if (all_visible)
                        valid = true;
                  else
                  {
                        HeapTupleData loctup;

                        loctup.t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
                        loctup.t_len = ItemIdGetLength(lpp);
                        ItemPointerSet(&(loctup.t_self), page, lineoff);

                        valid = HeapTupleSatisfiesVisibility(&loctup, snapshot, buffer);
                  }
                  if (valid)
                        scan->rs_vistuples[ntup++] = lineoff;
            }
      }

      LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

      Assert(ntup <= MaxHeapTuplesPerPage);
      scan->rs_ntuples = ntup;
}

/* ----------------
 *          heapgettup - fetch next heap tuple
 *
 *          Initialize the scan if not already done; then advance to the next
 *          tuple as indicated by "dir"; return the next tuple in scan->rs_ctup,
 *          or set scan->rs_ctup.t_data = NULL if no more tuples.
 *
 * dir == NoMovementScanDirection means "re-fetch the tuple indicated
 * by scan->rs_ctup".
 *
 * Note: the reason nkeys/key are passed separately, even though they are
 * kept in the scan descriptor, is that the caller may not want us to check
 * the scankeys.
 *
 * Note: when we fall off the end of the scan in either direction, we
 * reset rs_inited.  This means that a further request with the same
 * scan direction will restart the scan, which is a bit odd, but a
 * request with the opposite scan direction will start a fresh scan
 * in the proper direction.  The latter is required behavior for cursors,
 * while the former case is generally undefined behavior in Postgres
 * so we don't care too much.
 * ----------------
 */
static void
heapgettup(HeapScanDesc scan,
               ScanDirection dir,
               int nkeys,
               ScanKey key)
{
      HeapTuple   tuple = &(scan->rs_ctup);
      Snapshot    snapshot = scan->rs_snapshot;
      bool        backward = ScanDirectionIsBackward(dir);
      BlockNumber page;
      bool        finished;
      Page        dp;
      int               lines;
      OffsetNumber lineoff;
      int               linesleft;
      ItemId            lpp;

      /*
       * calculate next starting lineoff, given scan direction
       */
      if (ScanDirectionIsForward(dir))
      {
            if (!scan->rs_inited)
            {
                  /*
                   * return null immediately if relation is empty
                   */
                  if (scan->rs_nblocks == 0)
                  {
                        Assert(!BufferIsValid(scan->rs_cbuf));
                        tuple->t_data = NULL;
                        return;
                  }
                  page = scan->rs_startblock; /* first page */
                  heapgetpage(scan, page);
                  lineoff = FirstOffsetNumber;        /* first offnum */
                  scan->rs_inited = true;
            }
            else
            {
                  /* continue from previously returned page/tuple */
                  page = scan->rs_cblock;       /* current page */
                  lineoff =               /* next offnum */
                        OffsetNumberNext(ItemPointerGetOffsetNumber(&(tuple->t_self)));
            }

            LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);

            dp = (Page) BufferGetPage(scan->rs_cbuf);
            lines = PageGetMaxOffsetNumber(dp);
            /* page and lineoff now reference the physically next tid */

            linesleft = lines - lineoff + 1;
      }
      else if (backward)
      {
            if (!scan->rs_inited)
            {
                  /*
                   * return null immediately if relation is empty
                   */
                  if (scan->rs_nblocks == 0)
                  {
                        Assert(!BufferIsValid(scan->rs_cbuf));
                        tuple->t_data = NULL;
                        return;
                  }

                  /*
                   * Disable reporting to syncscan logic in a backwards scan; it's
                   * not very likely anyone else is doing the same thing at the same
                   * time, and much more likely that we'll just bollix things for
                   * forward scanners.
                   */
                  scan->rs_syncscan = false;
                  /* start from last page of the scan */
                  if (scan->rs_startblock > 0)
                        page = scan->rs_startblock - 1;
                  else
                        page = scan->rs_nblocks - 1;
                  heapgetpage(scan, page);
            }
            else
            {
                  /* continue from previously returned page/tuple */
                  page = scan->rs_cblock;       /* current page */
            }

            LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);

            dp = (Page) BufferGetPage(scan->rs_cbuf);
            lines = PageGetMaxOffsetNumber(dp);

            if (!scan->rs_inited)
            {
                  lineoff = lines;  /* final offnum */
                  scan->rs_inited = true;
            }
            else
            {
                  lineoff =               /* previous offnum */
                        OffsetNumberPrev(ItemPointerGetOffsetNumber(&(tuple->t_self)));
            }
            /* page and lineoff now reference the physically previous tid */

            linesleft = lineoff;
      }
      else
      {
            /*
             * ``no movement'' scan direction: refetch prior tuple
             */
            if (!scan->rs_inited)
            {
                  Assert(!BufferIsValid(scan->rs_cbuf));
                  tuple->t_data = NULL;
                  return;
            }

            page = ItemPointerGetBlockNumber(&(tuple->t_self));
            if (page != scan->rs_cblock)
                  heapgetpage(scan, page);

            /* Since the tuple was previously fetched, needn't lock page here */
            dp = (Page) BufferGetPage(scan->rs_cbuf);
            lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
            lpp = PageGetItemId(dp, lineoff);
            Assert(ItemIdIsNormal(lpp));

            tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
            tuple->t_len = ItemIdGetLength(lpp);

            return;
      }

      /*
       * advance the scan until we find a qualifying tuple or run out of stuff
       * to scan
       */
      lpp = PageGetItemId(dp, lineoff);
      for (;;)
      {
            while (linesleft > 0)
            {
                  if (ItemIdIsNormal(lpp))
                  {
                        bool        valid;

                        tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
                        tuple->t_len = ItemIdGetLength(lpp);
                        ItemPointerSet(&(tuple->t_self), page, lineoff);

                        /*
                         * if current tuple qualifies, return it.
                         */
                        valid = HeapTupleSatisfiesVisibility(tuple,
                                                                               snapshot,
                                                                               scan->rs_cbuf);

                        if (valid && key != NULL)
                              HeapKeyTest(tuple, RelationGetDescr(scan->rs_rd),
                                                nkeys, key, valid);

                        if (valid)
                        {
                              LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);
                              return;
                        }
                  }

                  /*
                   * otherwise move to the next item on the page
                   */
                  --linesleft;
                  if (backward)
                  {
                        --lpp;                  /* move back in this page's ItemId array */
                        --lineoff;
                  }
                  else
                  {
                        ++lpp;                  /* move forward in this page's ItemId array */
                        ++lineoff;
                  }
            }

            /*
             * if we get here, it means we've exhausted the items on this page and
             * it's time to move to the next.
             */
            LockBuffer(scan->rs_cbuf, BUFFER_LOCK_UNLOCK);

            /*
             * advance to next/prior page and detect end of scan
             */
            if (backward)
            {
                  finished = (page == scan->rs_startblock);
                  if (page == 0)
                        page = scan->rs_nblocks;
                  page--;
            }
            else
            {
                  page++;
                  if (page >= scan->rs_nblocks)
                        page = 0;
                  finished = (page == scan->rs_startblock);

                  /*
                   * Report our new scan position for synchronization purposes. We
                   * don't do that when moving backwards, however. That would just
                   * mess up any other forward-moving scanners.
                   *
                   * Note: we do this before checking for end of scan so that the
                   * final state of the position hint is back at the start of the
                   * rel.  That's not strictly necessary, but otherwise when you run
                   * the same query multiple times the starting position would shift
                   * a little bit backwards on every invocation, which is confusing.
                   * We don't guarantee any specific ordering in general, though.
                   */
                  if (scan->rs_syncscan)
                        ss_report_location(scan->rs_rd, page);
            }

            /*
             * return NULL if we've exhausted all the pages
             */
            if (finished)
            {
                  if (BufferIsValid(scan->rs_cbuf))
                        ReleaseBuffer(scan->rs_cbuf);
                  scan->rs_cbuf = InvalidBuffer;
                  scan->rs_cblock = InvalidBlockNumber;
                  tuple->t_data = NULL;
                  scan->rs_inited = false;
                  return;
            }

            heapgetpage(scan, page);

            LockBuffer(scan->rs_cbuf, BUFFER_LOCK_SHARE);

            dp = (Page) BufferGetPage(scan->rs_cbuf);
            lines = PageGetMaxOffsetNumber((Page) dp);
            linesleft = lines;
            if (backward)
            {
                  lineoff = lines;
                  lpp = PageGetItemId(dp, lines);
            }
            else
            {
                  lineoff = FirstOffsetNumber;
                  lpp = PageGetItemId(dp, FirstOffsetNumber);
            }
      }
}

/* ----------------
 *          heapgettup_pagemode - fetch next heap tuple in page-at-a-time mode
 *
 *          Same API as heapgettup, but used in page-at-a-time mode
 *
 * The internal logic is much the same as heapgettup's too, but there are some
 * differences: we do not take the buffer content lock (that only needs to
 * happen inside heapgetpage), and we iterate through just the tuples listed
 * in rs_vistuples[] rather than all tuples on the page.  Notice that
 * lineindex is 0-based, where the corresponding loop variable lineoff in
 * heapgettup is 1-based.
 * ----------------
 */
static void
heapgettup_pagemode(HeapScanDesc scan,
                              ScanDirection dir,
                              int nkeys,
                              ScanKey key)
{
      HeapTuple   tuple = &(scan->rs_ctup);
      bool        backward = ScanDirectionIsBackward(dir);
      BlockNumber page;
      bool        finished;
      Page        dp;
      int               lines;
      int               lineindex;
      OffsetNumber lineoff;
      int               linesleft;
      ItemId            lpp;

      /*
       * calculate next starting lineindex, given scan direction
       */
      if (ScanDirectionIsForward(dir))
      {
            if (!scan->rs_inited)
            {
                  /*
                   * return null immediately if relation is empty
                   */
                  if (scan->rs_nblocks == 0)
                  {
                        Assert(!BufferIsValid(scan->rs_cbuf));
                        tuple->t_data = NULL;
                        return;
                  }
                  page = scan->rs_startblock; /* first page */
                  heapgetpage(scan, page);
                  lineindex = 0;
                  scan->rs_inited = true;
            }
            else
            {
                  /* continue from previously returned page/tuple */
                  page = scan->rs_cblock;       /* current page */
                  lineindex = scan->rs_cindex + 1;
            }

            dp = (Page) BufferGetPage(scan->rs_cbuf);
            lines = scan->rs_ntuples;
            /* page and lineindex now reference the next visible tid */

            linesleft = lines - lineindex;
      }
      else if (backward)
      {
            if (!scan->rs_inited)
            {
                  /*
                   * return null immediately if relation is empty
                   */
                  if (scan->rs_nblocks == 0)
                  {
                        Assert(!BufferIsValid(scan->rs_cbuf));
                        tuple->t_data = NULL;
                        return;
                  }

                  /*
                   * Disable reporting to syncscan logic in a backwards scan; it's
                   * not very likely anyone else is doing the same thing at the same
                   * time, and much more likely that we'll just bollix things for
                   * forward scanners.
                   */
                  scan->rs_syncscan = false;
                  /* start from last page of the scan */
                  if (scan->rs_startblock > 0)
                        page = scan->rs_startblock - 1;
                  else
                        page = scan->rs_nblocks - 1;
                  heapgetpage(scan, page);
            }
            else
            {
                  /* continue from previously returned page/tuple */
                  page = scan->rs_cblock;       /* current page */
            }

            dp = (Page) BufferGetPage(scan->rs_cbuf);
            lines = scan->rs_ntuples;

            if (!scan->rs_inited)
            {
                  lineindex = lines - 1;
                  scan->rs_inited = true;
            }
            else
            {
                  lineindex = scan->rs_cindex - 1;
            }
            /* page and lineindex now reference the previous visible tid */

            linesleft = lineindex + 1;
      }
      else
      {
            /*
             * ``no movement'' scan direction: refetch prior tuple
             */
            if (!scan->rs_inited)
            {
                  Assert(!BufferIsValid(scan->rs_cbuf));
                  tuple->t_data = NULL;
                  return;
            }

            page = ItemPointerGetBlockNumber(&(tuple->t_self));
            if (page != scan->rs_cblock)
                  heapgetpage(scan, page);

            /* Since the tuple was previously fetched, needn't lock page here */
            dp = (Page) BufferGetPage(scan->rs_cbuf);
            lineoff = ItemPointerGetOffsetNumber(&(tuple->t_self));
            lpp = PageGetItemId(dp, lineoff);
            Assert(ItemIdIsNormal(lpp));

            tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
            tuple->t_len = ItemIdGetLength(lpp);

            /* check that rs_cindex is in sync */
            Assert(scan->rs_cindex < scan->rs_ntuples);
            Assert(lineoff == scan->rs_vistuples[scan->rs_cindex]);

            return;
      }

      /*
       * advance the scan until we find a qualifying tuple or run out of stuff
       * to scan
       */
      for (;;)
      {
            while (linesleft > 0)
            {
                  lineoff = scan->rs_vistuples[lineindex];
                  lpp = PageGetItemId(dp, lineoff);
                  Assert(ItemIdIsNormal(lpp));

                  tuple->t_data = (HeapTupleHeader) PageGetItem((Page) dp, lpp);
                  tuple->t_len = ItemIdGetLength(lpp);
                  ItemPointerSet(&(tuple->t_self), page, lineoff);

                  /*
                   * if current tuple qualifies, return it.
                   */
                  if (key != NULL)
                  {
                        bool        valid;

                        HeapKeyTest(tuple, RelationGetDescr(scan->rs_rd),
                                          nkeys, key, valid);
                        if (valid)
                        {
                              scan->rs_cindex = lineindex;
                              return;
                        }
                  }
                  else
                  {
                        scan->rs_cindex = lineindex;
                        return;
                  }

                  /*
                   * otherwise move to the next item on the page
                   */
                  --linesleft;
                  if (backward)
                        --lineindex;
                  else
                        ++lineindex;
            }

            /*
             * if we get here, it means we've exhausted the items on this page and
             * it's time to move to the next.
             */
            if (backward)
            {
                  finished = (page == scan->rs_startblock);
                  if (page == 0)
                        page = scan->rs_nblocks;
                  page--;
            }
            else
            {
                  page++;
                  if (page >= scan->rs_nblocks)
                        page = 0;
                  finished = (page == scan->rs_startblock);

                  /*
                   * Report our new scan position for synchronization purposes. We
                   * don't do that when moving backwards, however. That would just
                   * mess up any other forward-moving scanners.
                   *
                   * Note: we do this before checking for end of scan so that the
                   * final state of the position hint is back at the start of the
                   * rel.  That's not strictly necessary, but otherwise when you run
                   * the same query multiple times the starting position would shift
                   * a little bit backwards on every invocation, which is confusing.
                   * We don't guarantee any specific ordering in general, though.
                   */
                  if (scan->rs_syncscan)
                        ss_report_location(scan->rs_rd, page);
            }

            /*
             * return NULL if we've exhausted all the pages
             */
            if (finished)
            {
                  if (BufferIsValid(scan->rs_cbuf))
                        ReleaseBuffer(scan->rs_cbuf);
                  scan->rs_cbuf = InvalidBuffer;
                  scan->rs_cblock = InvalidBlockNumber;
                  tuple->t_data = NULL;
                  scan->rs_inited = false;
                  return;
            }

            heapgetpage(scan, page);

            dp = (Page) BufferGetPage(scan->rs_cbuf);
            lines = scan->rs_ntuples;
            linesleft = lines;
            if (backward)
                  lineindex = lines - 1;
            else
                  lineindex = 0;
      }
}


#if defined(DISABLE_COMPLEX_MACRO)
/*
 * This is formatted so oddly so that the correspondence to the macro
 * definition in access/heapam.h is maintained.
 */
Datum
fastgetattr(HeapTuple tup, int attnum, TupleDesc tupleDesc,
                  bool *isnull)
{
      return (
                  (attnum) > 0 ?
                  (
                   ((isnull) ? (*(isnull) = false) : (dummyret) NULL),
                   HeapTupleNoNulls(tup) ?
                   (
                    (tupleDesc)->attrs[(attnum) - 1]->attcacheoff >= 0 ?
                    (
                     fetchatt((tupleDesc)->attrs[(attnum) - 1],
                                    (char *) (tup)->t_data + (tup)->t_data->t_hoff +
                                    (tupleDesc)->attrs[(attnum) - 1]->attcacheoff)
                     )
                    :
                    nocachegetattr((tup), (attnum), (tupleDesc), (isnull))
                    )
                   :
                   (
                    att_isnull((attnum) - 1, (tup)->t_data->t_bits) ?
                    (
                     ((isnull) ? (*(isnull) = true) : (dummyret) NULL),
                     (Datum) NULL
                     )
                    :
                    (
                     nocachegetattr((tup), (attnum), (tupleDesc), (isnull))
                     )
                    )
                   )
                  :
                  (
                   (Datum) NULL
                   )
            );
}
#endif   /* defined(DISABLE_COMPLEX_MACRO) */


/* ----------------------------------------------------------------
 *                             heap access method interface
 * ----------------------------------------------------------------
 */

/* ----------------
 *          relation_open - open any relation by relation OID
 *
 *          If lockmode is not "NoLock", the specified kind of lock is
 *          obtained on the relation.  (Generally, NoLock should only be
 *          used if the caller knows it has some appropriate lock on the
 *          relation already.)
 *
 *          An error is raised if the relation does not exist.
 *
 *          NB: a "relation" is anything with a pg_class entry.  The caller is
 *          expected to check whether the relkind is something it can handle.
 * ----------------
 */
Relation
relation_open(Oid relationId, LOCKMODE lockmode)
{
      Relation    r;

      Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);

      /* Get the lock before trying to open the relcache entry */
      if (lockmode != NoLock)
            LockRelationOid(relationId, lockmode);

      /* The relcache does all the real work... */
      r = RelationIdGetRelation(relationId);

      if (!RelationIsValid(r))
            elog(ERROR, "could not open relation with OID %u", relationId);

      /* Make note that we've accessed a temporary relation */
      if (r->rd_istemp)
            MyXactAccessedTempRel = true;

      pgstat_initstats(r);

      return r;
}

/* ----------------
 *          try_relation_open - open any relation by relation OID
 *
 *          Same as relation_open, except return NULL instead of failing
 *          if the relation does not exist.
 * ----------------
 */
Relation
try_relation_open(Oid relationId, LOCKMODE lockmode)
{
      Relation    r;

      Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);

      /* Get the lock first */
      if (lockmode != NoLock)
            LockRelationOid(relationId, lockmode);

      /*
       * Now that we have the lock, probe to see if the relation really exists
       * or not.
       */
      if (!SearchSysCacheExists(RELOID,
                                            ObjectIdGetDatum(relationId),
                                            0, 0, 0))
      {
            /* Release useless lock */
            if (lockmode != NoLock)
                  UnlockRelationOid(relationId, lockmode);

            return NULL;
      }

      /* Should be safe to do a relcache load */
      r = RelationIdGetRelation(relationId);

      if (!RelationIsValid(r))
            elog(ERROR, "could not open relation with OID %u", relationId);

      /* Make note that we've accessed a temporary relation */
      if (r->rd_istemp)
            MyXactAccessedTempRel = true;

      pgstat_initstats(r);

      return r;
}

/* ----------------
 *          relation_openrv - open any relation specified by a RangeVar
 *
 *          Same as relation_open, but the relation is specified by a RangeVar.
 * ----------------
 */
Relation
relation_openrv(const RangeVar *relation, LOCKMODE lockmode)
{
      Oid               relOid;

      /*
       * Check for shared-cache-inval messages before trying to open the
       * relation.  This is needed to cover the case where the name identifies a
       * rel that has been dropped and recreated since the start of our
       * transaction: if we don't flush the old syscache entry then we'll latch
       * onto that entry and suffer an error when we do RelationIdGetRelation.
       * Note that relation_open does not need to do this, since a relation's
       * OID never changes.
       *
       * We skip this if asked for NoLock, on the assumption that the caller has
       * already ensured some appropriate lock is held.
       */
      if (lockmode != NoLock)
            AcceptInvalidationMessages();

      /* Look up the appropriate relation using namespace search */
      relOid = RangeVarGetRelid(relation, false);

      /* Let relation_open do the rest */
      return relation_open(relOid, lockmode);
}

/* ----------------
 *          try_relation_openrv - open any relation specified by a RangeVar
 *
 *          Same as relation_openrv, but return NULL instead of failing for
 *          relation-not-found.  (Note that some other causes, such as
 *          permissions problems, will still result in an ereport.)
 * ----------------
 */
Relation
try_relation_openrv(const RangeVar *relation, LOCKMODE lockmode)
{
      Oid               relOid;

      /*
       * Check for shared-cache-inval messages before trying to open the
       * relation.  This is needed to cover the case where the name identifies a
       * rel that has been dropped and recreated since the start of our
       * transaction: if we don't flush the old syscache entry then we'll latch
       * onto that entry and suffer an error when we do RelationIdGetRelation.
       * Note that relation_open does not need to do this, since a relation's
       * OID never changes.
       *
       * We skip this if asked for NoLock, on the assumption that the caller has
       * already ensured some appropriate lock is held.
       */
      if (lockmode != NoLock)
            AcceptInvalidationMessages();

      /* Look up the appropriate relation using namespace search */
      relOid = RangeVarGetRelid(relation, true);

      /* Return NULL on not-found */
      if (!OidIsValid(relOid))
            return NULL;

      /* Let relation_open do the rest */
      return relation_open(relOid, lockmode);
}

/* ----------------
 *          relation_close - close any relation
 *
 *          If lockmode is not "NoLock", we then release the specified lock.
 *
 *          Note that it is often sensible to hold a lock beyond relation_close;
 *          in that case, the lock is released automatically at xact end.
 * ----------------
 */
void
relation_close(Relation relation, LOCKMODE lockmode)
{
      LockRelId   relid = relation->rd_lockInfo.lockRelId;

      Assert(lockmode >= NoLock && lockmode < MAX_LOCKMODES);

      /* The relcache does the real work... */
      RelationClose(relation);

      if (lockmode != NoLock)
            UnlockRelationId(&relid, lockmode);
}


/* ----------------
 *          heap_open - open a heap relation by relation OID
 *
 *          This is essentially relation_open plus check that the relation
 *          is not an index nor a composite type.  (The caller should also
 *          check that it's not a view before assuming it has storage.)
 * ----------------
 */
Relation
heap_open(Oid relationId, LOCKMODE lockmode)
{
      Relation    r;

      r = relation_open(relationId, lockmode);

      if (r->rd_rel->relkind == RELKIND_INDEX)
            ereport(ERROR,
                        (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                         errmsg("\"%s\" is an index",
                                    RelationGetRelationName(r))));
      else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
            ereport(ERROR,
                        (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                         errmsg("\"%s\" is a composite type",
                                    RelationGetRelationName(r))));

      return r;
}

/* ----------------
 *          heap_openrv - open a heap relation specified
 *          by a RangeVar node
 *
 *          As above, but relation is specified by a RangeVar.
 * ----------------
 */
Relation
heap_openrv(const RangeVar *relation, LOCKMODE lockmode)
{
      Relation    r;

      r = relation_openrv(relation, lockmode);

      if (r->rd_rel->relkind == RELKIND_INDEX)
            ereport(ERROR,
                        (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                         errmsg("\"%s\" is an index",
                                    RelationGetRelationName(r))));
      else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
            ereport(ERROR,
                        (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                         errmsg("\"%s\" is a composite type",
                                    RelationGetRelationName(r))));

      return r;
}

/* ----------------
 *          try_heap_openrv - open a heap relation specified
 *          by a RangeVar node
 *
 *          As above, but return NULL instead of failing for relation-not-found.
 * ----------------
 */
Relation
try_heap_openrv(const RangeVar *relation, LOCKMODE lockmode)
{
      Relation    r;

      r = try_relation_openrv(relation, lockmode);

      if (r)
      {
            if (r->rd_rel->relkind == RELKIND_INDEX)
                  ereport(ERROR,
                              (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                               errmsg("\"%s\" is an index",
                                          RelationGetRelationName(r))));
            else if (r->rd_rel->relkind == RELKIND_COMPOSITE_TYPE)
                  ereport(ERROR,
                              (errcode(ERRCODE_WRONG_OBJECT_TYPE),
                               errmsg("\"%s\" is a composite type",
                                          RelationGetRelationName(r))));
      }

      return r;
}


/* ----------------
 *          heap_beginscan    - begin relation scan
 *
 * heap_beginscan_strat offers an extended API that lets the caller control
 * whether a nondefault buffer access strategy can be used, and whether
 * syncscan can be chosen (possibly resulting in the scan not starting from
 * block zero).  Both of these default to TRUE with plain heap_beginscan.
 *
 * heap_beginscan_bm is an alternative entry point for setting up a
 * HeapScanDesc for a bitmap heap scan.  Although that scan technology is
 * really quite unlike a standard seqscan, there is just enough commonality
 * to make it worth using the same data structure.
 * ----------------
 */
HeapScanDesc
heap_beginscan(Relation relation, Snapshot snapshot,
                     int nkeys, ScanKey key)
{
      return heap_beginscan_internal(relation, snapshot, nkeys, key,
                                                   true, true, false);
}

HeapScanDesc
heap_beginscan_strat(Relation relation, Snapshot snapshot,
                               int nkeys, ScanKey key,
                               bool allow_strat, bool allow_sync)
{
      return heap_beginscan_internal(relation, snapshot, nkeys, key,
                                                   allow_strat, allow_sync, false);
}

HeapScanDesc
heap_beginscan_bm(Relation relation, Snapshot snapshot,
                          int nkeys, ScanKey key)
{
      return heap_beginscan_internal(relation, snapshot, nkeys, key,
                                                   false, false, true);
}

static HeapScanDesc
heap_beginscan_internal(Relation relation, Snapshot snapshot,
                                    int nkeys, ScanKey key,
                                    bool allow_strat, bool allow_sync,
                                    bool is_bitmapscan)
{
      HeapScanDesc scan;

      /*
       * increment relation ref count while scanning relation
       *
       * This is just to make really sure the relcache entry won't go away while
       * the scan has a pointer to it.  Caller should be holding the rel open
       * anyway, so this is redundant in all normal scenarios...
       */
      RelationIncrementReferenceCount(relation);

      /*
       * allocate and initialize scan descriptor
       */
      scan = (HeapScanDesc) palloc(sizeof(HeapScanDescData));

      scan->rs_rd = relation;
      scan->rs_snapshot = snapshot;
      scan->rs_nkeys = nkeys;
      scan->rs_bitmapscan = is_bitmapscan;
      scan->rs_strategy = NULL;     /* set in initscan */
      scan->rs_allow_strat = allow_strat;
      scan->rs_allow_sync = allow_sync;

      /*
       * we can use page-at-a-time mode if it's an MVCC-safe snapshot
       */
      scan->rs_pageatatime = IsMVCCSnapshot(snapshot);

      /* we only need to set this up once */
      scan->rs_ctup.t_tableOid = RelationGetRelid(relation);

      /*
       * we do this here instead of in initscan() because heap_rescan also calls
       * initscan() and we don't want to allocate memory again
       */
      if (nkeys > 0)
            scan->rs_key = (ScanKey) palloc(sizeof(ScanKeyData) * nkeys);
      else
            scan->rs_key = NULL;

      initscan(scan, key, false);

      return scan;
}

/* ----------------
 *          heap_rescan       - restart a relation scan
 * ----------------
 */
void
heap_rescan(HeapScanDesc scan,
                  ScanKey key)
{
      /*
       * unpin scan buffers
       */
      if (BufferIsValid(scan->rs_cbuf))
            ReleaseBuffer(scan->rs_cbuf);

      /*
       * reinitialize scan descriptor
       */
      initscan(scan, key, true);
}

/* ----------------
 *          heap_endscan      - end relation scan
 *
 *          See how to integrate with index scans.
 *          Check handling if reldesc caching.
 * ----------------
 */
void
heap_endscan(HeapScanDesc scan)
{
      /* Note: no locking manipulations needed */

      /*
       * unpin scan buffers
       */
      if (BufferIsValid(scan->rs_cbuf))
            ReleaseBuffer(scan->rs_cbuf);

      /*
       * decrement relation reference count and free scan descriptor storage
       */
      RelationDecrementReferenceCount(scan->rs_rd);

      if (scan->rs_key)
            pfree(scan->rs_key);

      if (scan->rs_strategy != NULL)
            FreeAccessStrategy(scan->rs_strategy);

      pfree(scan);
}

/* ----------------
 *          heap_getnext      - retrieve next tuple in scan
 *
 *          Fix to work with index relations.
 *          We don't return the buffer anymore, but you can get it from the
 *          returned HeapTuple.
 * ----------------
 */

#ifdef HEAPDEBUGALL
#define HEAPDEBUG_1 \
      elog(DEBUG2, "heap_getnext([%s,nkeys=%d],dir=%d) called", \
             RelationGetRelationName(scan->rs_rd), scan->rs_nkeys, (int) direction)
#define HEAPDEBUG_2 \
      elog(DEBUG2, "heap_getnext returning EOS")
#define HEAPDEBUG_3 \
      elog(DEBUG2, "heap_getnext returning tuple")
#else
#define HEAPDEBUG_1
#define HEAPDEBUG_2
#define HEAPDEBUG_3
#endif   /* !defined(HEAPDEBUGALL) */


HeapTuple
heap_getnext(HeapScanDesc scan, ScanDirection direction)
{
      /* Note: no locking manipulations needed */

      HEAPDEBUG_1;                        /* heap_getnext( info ) */

      if (scan->rs_pageatatime)
            heapgettup_pagemode(scan, direction,
                                          scan->rs_nkeys, scan->rs_key);
      else
            heapgettup(scan, direction, scan->rs_nkeys, scan->rs_key);

      if (scan->rs_ctup.t_data == NULL)
      {
            HEAPDEBUG_2;                  /* heap_getnext returning EOS */
            return NULL;
      }

      /*
       * if we get here it means we have a new current scan tuple, so point to
       * the proper return buffer and return the tuple.
       */
      HEAPDEBUG_3;                        /* heap_getnext returning tuple */

      pgstat_count_heap_getnext(scan->rs_rd);

      return &(scan->rs_ctup);
}

/*
 *    heap_fetch        - retrieve tuple with given tid
 *
 * On entry, tuple->t_self is the TID to fetch.  We pin the buffer holding
 * the tuple, fill in the remaining fields of *tuple, and check the tuple
 * against the specified snapshot.
 *
 * If successful (tuple found and passes snapshot time qual), then *userbuf
 * is set to the buffer holding the tuple and TRUE is returned.  The caller
 * must unpin the buffer when done with the tuple.
 *
 * If the tuple is not found (ie, item number references a deleted slot),
 * then tuple->t_data is set to NULL and FALSE is returned.
 *
 * If the tuple is found but fails the time qual check, then FALSE is returned
 * but tuple->t_data is left pointing to the tuple.
 *
 * keep_buf determines what is done with the buffer in the FALSE-result cases.
 * When the caller specifies keep_buf = true, we retain the pin on the buffer
 * and return it in *userbuf (so the caller must eventually unpin it); when
 * keep_buf = false, the pin is released and *userbuf is set to InvalidBuffer.
 *
 * stats_relation is the relation to charge the heap_fetch operation against
 * for statistical purposes.  (This could be the heap rel itself, an
 * associated index, or NULL to not count the fetch at all.)
 *
 * heap_fetch does not follow HOT chains: only the exact TID requested will
 * be fetched.
 *
 * It is somewhat inconsistent that we ereport() on invalid block number but
 * return false on invalid item number.  There are a couple of reasons though.
 * One is that the caller can relatively easily check the block number for
 * validity, but cannot check the item number without reading the page
 * himself.  Another is that when we are following a t_ctid link, we can be
 * reasonably confident that the page number is valid (since VACUUM shouldn't
 * truncate off the destination page without having killed the referencing
 * tuple first), but the item number might well not be good.
 */
bool
heap_fetch(Relation relation,
               Snapshot snapshot,
               HeapTuple tuple,
               Buffer *userbuf,
               bool keep_buf,
               Relation stats_relation)
{
      ItemPointer tid = &(tuple->t_self);
      ItemId            lp;
      Buffer            buffer;
      Page        page;
      OffsetNumber offnum;
      bool        valid;

      /*
       * Fetch and pin the appropriate page of the relation.
       */
      buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));

      /*
       * Need share lock on buffer to examine tuple commit status.
       */
      LockBuffer(buffer, BUFFER_LOCK_SHARE);
      page = BufferGetPage(buffer);

      /*
       * We'd better check for out-of-range offnum in case of VACUUM since the
       * TID was obtained.
       */
      offnum = ItemPointerGetOffsetNumber(tid);
      if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
      {
            LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
            if (keep_buf)
                  *userbuf = buffer;
            else
            {
                  ReleaseBuffer(buffer);
                  *userbuf = InvalidBuffer;
            }
            tuple->t_data = NULL;
            return false;
      }

      /*
       * get the item line pointer corresponding to the requested tid
       */
      lp = PageGetItemId(page, offnum);

      /*
       * Must check for deleted tuple.
       */
      if (!ItemIdIsNormal(lp))
      {
            LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
            if (keep_buf)
                  *userbuf = buffer;
            else
            {
                  ReleaseBuffer(buffer);
                  *userbuf = InvalidBuffer;
            }
            tuple->t_data = NULL;
            return false;
      }

      /*
       * fill in *tuple fields
       */
      tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
      tuple->t_len = ItemIdGetLength(lp);
      tuple->t_tableOid = RelationGetRelid(relation);

      /*
       * check time qualification of tuple, then release lock
       */
      valid = HeapTupleSatisfiesVisibility(tuple, snapshot, buffer);

      LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

      if (valid)
      {
            /*
             * All checks passed, so return the tuple as valid. Caller is now
             * responsible for releasing the buffer.
             */
            *userbuf = buffer;

            /* Count the successful fetch against appropriate rel, if any */
            if (stats_relation != NULL)
                  pgstat_count_heap_fetch(stats_relation);

            return true;
      }

      /* Tuple failed time qual, but maybe caller wants to see it anyway. */
      if (keep_buf)
            *userbuf = buffer;
      else
      {
            ReleaseBuffer(buffer);
            *userbuf = InvalidBuffer;
      }

      return false;
}

/*
 *    heap_hot_search_buffer  - search HOT chain for tuple satisfying snapshot
 *
 * On entry, *tid is the TID of a tuple (either a simple tuple, or the root
 * of a HOT chain), and buffer is the buffer holding this tuple.  We search
 * for the first chain member satisfying the given snapshot.  If one is
 * found, we update *tid to reference that tuple's offset number, and
 * return TRUE.  If no match, return FALSE without modifying *tid.
 *
 * If all_dead is not NULL, we check non-visible tuples to see if they are
 * globally dead; *all_dead is set TRUE if all members of the HOT chain
 * are vacuumable, FALSE if not.
 *
 * Unlike heap_fetch, the caller must already have pin and (at least) share
 * lock on the buffer; it is still pinned/locked at exit.  Also unlike
 * heap_fetch, we do not report any pgstats count; caller may do so if wanted.
 */
bool
heap_hot_search_buffer(ItemPointer tid, Buffer buffer, Snapshot snapshot,
                                 bool *all_dead)
{
      Page        dp = (Page) BufferGetPage(buffer);
      TransactionId prev_xmax = InvalidTransactionId;
      OffsetNumber offnum;
      bool        at_chain_start;

      if (all_dead)
            *all_dead = true;

      Assert(TransactionIdIsValid(RecentGlobalXmin));

      Assert(ItemPointerGetBlockNumber(tid) == BufferGetBlockNumber(buffer));
      offnum = ItemPointerGetOffsetNumber(tid);
      at_chain_start = true;

      /* Scan through possible multiple members of HOT-chain */
      for (;;)
      {
            ItemId            lp;
            HeapTupleData heapTuple;

            /* check for bogus TID */
            if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(dp))
                  break;

            lp = PageGetItemId(dp, offnum);

            /* check for unused, dead, or redirected items */
            if (!ItemIdIsNormal(lp))
            {
                  /* We should only see a redirect at start of chain */
                  if (ItemIdIsRedirected(lp) && at_chain_start)
                  {
                        /* Follow the redirect */
                        offnum = ItemIdGetRedirect(lp);
                        at_chain_start = false;
                        continue;
                  }
                  /* else must be end of chain */
                  break;
            }

            heapTuple.t_data = (HeapTupleHeader) PageGetItem(dp, lp);
            heapTuple.t_len = ItemIdGetLength(lp);

            /*
             * Shouldn't see a HEAP_ONLY tuple at chain start.
             */
            if (at_chain_start && HeapTupleIsHeapOnly(&heapTuple))
                  break;

            /*
             * The xmin should match the previous xmax value, else chain is
             * broken.
             */
            if (TransactionIdIsValid(prev_xmax) &&
                  !TransactionIdEquals(prev_xmax,
                                                 HeapTupleHeaderGetXmin(heapTuple.t_data)))
                  break;

            /* If it's visible per the snapshot, we must return it */
            if (HeapTupleSatisfiesVisibility(&heapTuple, snapshot, buffer))
            {
                  ItemPointerSetOffsetNumber(tid, offnum);
                  if (all_dead)
                        *all_dead = false;
                  return true;
            }

            /*
             * If we can't see it, maybe no one else can either.  At caller
             * request, check whether all chain members are dead to all
             * transactions.
             */
            if (all_dead && *all_dead &&
                  HeapTupleSatisfiesVacuum(heapTuple.t_data, RecentGlobalXmin,
                                                       buffer) != HEAPTUPLE_DEAD)
                  *all_dead = false;

            /*
             * Check to see if HOT chain continues past this tuple; if so fetch
             * the next offnum and loop around.
             */
            if (HeapTupleIsHotUpdated(&heapTuple))
            {
                  Assert(ItemPointerGetBlockNumber(&heapTuple.t_data->t_ctid) ==
                           ItemPointerGetBlockNumber(tid));
                  offnum = ItemPointerGetOffsetNumber(&heapTuple.t_data->t_ctid);
                  at_chain_start = false;
                  prev_xmax = HeapTupleHeaderGetXmax(heapTuple.t_data);
            }
            else
                  break;                        /* end of chain */
      }

      return false;
}

/*
 *    heap_hot_search         - search HOT chain for tuple satisfying snapshot
 *
 * This has the same API as heap_hot_search_buffer, except that the caller
 * does not provide the buffer containing the page, rather we access it
 * locally.
 */
bool
heap_hot_search(ItemPointer tid, Relation relation, Snapshot snapshot,
                        bool *all_dead)
{
      bool        result;
      Buffer            buffer;

      buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
      LockBuffer(buffer, BUFFER_LOCK_SHARE);
      result = heap_hot_search_buffer(tid, buffer, snapshot, all_dead);
      LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
      ReleaseBuffer(buffer);
      return result;
}

/*
 *    heap_get_latest_tid -  get the latest tid of a specified tuple
 *
 * Actually, this gets the latest version that is visible according to
 * the passed snapshot.  You can pass SnapshotDirty to get the very latest,
 * possibly uncommitted version.
 *
 * *tid is both an input and an output parameter: it is updated to
 * show the latest version of the row.    Note that it will not be changed
 * if no version of the row passes the snapshot test.
 */
void
heap_get_latest_tid(Relation relation,
                              Snapshot snapshot,
                              ItemPointer tid)
{
      BlockNumber blk;
      ItemPointerData ctid;
      TransactionId priorXmax;

      /* this is to avoid Assert failures on bad input */
      if (!ItemPointerIsValid(tid))
            return;

      /*
       * Since this can be called with user-supplied TID, don't trust the input
       * too much.  (RelationGetNumberOfBlocks is an expensive check, so we
       * don't check t_ctid links again this way.  Note that it would not do to
       * call it just once and save the result, either.)
       */
      blk = ItemPointerGetBlockNumber(tid);
      if (blk >= RelationGetNumberOfBlocks(relation))
            elog(ERROR, "block number %u is out of range for relation \"%s\"",
                   blk, RelationGetRelationName(relation));

      /*
       * Loop to chase down t_ctid links.  At top of loop, ctid is the tuple we
       * need to examine, and *tid is the TID we will return if ctid turns out
       * to be bogus.
       *
       * Note that we will loop until we reach the end of the t_ctid chain.
       * Depending on the snapshot passed, there might be at most one visible
       * version of the row, but we don't try to optimize for that.
       */
      ctid = *tid;
      priorXmax = InvalidTransactionId;   /* cannot check first XMIN */
      for (;;)
      {
            Buffer            buffer;
            Page        page;
            OffsetNumber offnum;
            ItemId            lp;
            HeapTupleData tp;
            bool        valid;

            /*
             * Read, pin, and lock the page.
             */
            buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&ctid));
            LockBuffer(buffer, BUFFER_LOCK_SHARE);
            page = BufferGetPage(buffer);

            /*
             * Check for bogus item number.  This is not treated as an error
             * condition because it can happen while following a t_ctid link. We
             * just assume that the prior tid is OK and return it unchanged.
             */
            offnum = ItemPointerGetOffsetNumber(&ctid);
            if (offnum < FirstOffsetNumber || offnum > PageGetMaxOffsetNumber(page))
            {
                  UnlockReleaseBuffer(buffer);
                  break;
            }
            lp = PageGetItemId(page, offnum);
            if (!ItemIdIsNormal(lp))
            {
                  UnlockReleaseBuffer(buffer);
                  break;
            }

            /* OK to access the tuple */
            tp.t_self = ctid;
            tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
            tp.t_len = ItemIdGetLength(lp);

            /*
             * After following a t_ctid link, we might arrive at an unrelated
             * tuple.  Check for XMIN match.
             */
            if (TransactionIdIsValid(priorXmax) &&
              !TransactionIdEquals(priorXmax, HeapTupleHeaderGetXmin(tp.t_data)))
            {
                  UnlockReleaseBuffer(buffer);
                  break;
            }

            /*
             * Check time qualification of tuple; if visible, set it as the new
             * result candidate.
             */
            valid = HeapTupleSatisfiesVisibility(&tp, snapshot, buffer);
            if (valid)
                  *tid = ctid;

            /*
             * If there's a valid t_ctid link, follow it, else we're done.
             */
            if ((tp.t_data->t_infomask & (HEAP_XMAX_INVALID | HEAP_IS_LOCKED)) ||
                  ItemPointerEquals(&tp.t_self, &tp.t_data->t_ctid))
            {
                  UnlockReleaseBuffer(buffer);
                  break;
            }

            ctid = tp.t_data->t_ctid;
            priorXmax = HeapTupleHeaderGetXmax(tp.t_data);
            UnlockReleaseBuffer(buffer);
      }                                         /* end of loop */
}


/*
 * UpdateXmaxHintBits - update tuple hint bits after xmax transaction ends
 *
 * This is called after we have waited for the XMAX transaction to terminate.
 * If the transaction aborted, we guarantee the XMAX_INVALID hint bit will
 * be set on exit.      If the transaction committed, we set the XMAX_COMMITTED
 * hint bit if possible --- but beware that that may not yet be possible,
 * if the transaction committed asynchronously.  Hence callers should look
 * only at XMAX_INVALID.
 */
static void
UpdateXmaxHintBits(HeapTupleHeader tuple, Buffer buffer, TransactionId xid)
{
      Assert(TransactionIdEquals(HeapTupleHeaderGetXmax(tuple), xid));

      if (!(tuple->t_infomask & (HEAP_XMAX_COMMITTED | HEAP_XMAX_INVALID)))
      {
            if (TransactionIdDidCommit(xid))
                  HeapTupleSetHintBits(tuple, buffer, HEAP_XMAX_COMMITTED,
                                                 xid);
            else
                  HeapTupleSetHintBits(tuple, buffer, HEAP_XMAX_INVALID,
                                                 InvalidTransactionId);
      }
}


/*
 * GetBulkInsertState - prepare status object for a bulk insert
 */
BulkInsertState
GetBulkInsertState(void)
{
      BulkInsertState bistate;

      bistate = (BulkInsertState) palloc(sizeof(BulkInsertStateData));
      bistate->strategy = GetAccessStrategy(BAS_BULKWRITE);
      bistate->current_buf = InvalidBuffer;
      return bistate;
}

/*
 * FreeBulkInsertState - clean up after finishing a bulk insert
 */
void
FreeBulkInsertState(BulkInsertState bistate)
{
      if (bistate->current_buf != InvalidBuffer)
            ReleaseBuffer(bistate->current_buf);
      FreeAccessStrategy(bistate->strategy);
      pfree(bistate);
}


/*
 *    heap_insert       - insert tuple into a heap
 *
 * The new tuple is stamped with current transaction ID and the specified
 * command ID.
 *
 * If the HEAP_INSERT_SKIP_WAL option is specified, the new tuple is not
 * logged in WAL, even for a non-temp relation.  Safe usage of this behavior
 * requires that we arrange that all new tuples go into new pages not
 * containing any tuples from other transactions, and that the relation gets
 * fsync'd before commit.  (See also heap_sync() comments)
 *
 * The HEAP_INSERT_SKIP_FSM option is passed directly to
 * RelationGetBufferForTuple, which see for more info.
 *
 * Note that these options will be applied when inserting into the heap's
 * TOAST table, too, if the tuple requires any out-of-line data.
 *
 * The BulkInsertState object (if any; bistate can be NULL for default
 * behavior) is also just passed through to RelationGetBufferForTuple.
 *
 * The return value is the OID assigned to the tuple (either here or by the
 * caller), or InvalidOid if no OID.  The header fields of *tup are updated
 * to match the stored tuple; in particular tup->t_self receives the actual
 * TID where the tuple was stored.  But note that any toasting of fields
 * within the tuple data is NOT reflected into *tup.
 */
Oid
heap_insert(Relation relation, HeapTuple tup, CommandId cid,
                  int options, BulkInsertState bistate)
{
      TransactionId xid = GetCurrentTransactionId();
      HeapTuple   heaptup;
      Buffer            buffer;
      bool        all_visible_cleared = false;

      if (relation->rd_rel->relhasoids)
      {
#ifdef NOT_USED
            /* this is redundant with an Assert in HeapTupleSetOid */
            Assert(tup->t_data->t_infomask & HEAP_HASOID);
#endif

            /*
             * If the object id of this tuple has already been assigned, trust the
             * caller.  There are a couple of ways this can happen.  At initial db
             * creation, the backend program sets oids for tuples. When we define
             * an index, we set the oid.  Finally, in the future, we may allow
             * users to set their own object ids in order to support a persistent
             * object store (objects need to contain pointers to one another).
             */
            if (!OidIsValid(HeapTupleGetOid(tup)))
                  HeapTupleSetOid(tup, GetNewOid(relation));
      }
      else
      {
            /* check there is not space for an OID */
            Assert(!(tup->t_data->t_infomask & HEAP_HASOID));
      }

      tup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
      tup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
      tup->t_data->t_infomask |= HEAP_XMAX_INVALID;
      HeapTupleHeaderSetXmin(tup->t_data, xid);
      HeapTupleHeaderSetCmin(tup->t_data, cid);
      HeapTupleHeaderSetXmax(tup->t_data, 0);         /* for cleanliness */
      tup->t_tableOid = RelationGetRelid(relation);

      /*
       * If the new tuple is too big for storage or contains already toasted
       * out-of-line attributes from some other relation, invoke the toaster.
       *
       * Note: below this point, heaptup is the data we actually intend to store
       * into the relation; tup is the caller's original untoasted data.
       */
      if (relation->rd_rel->relkind != RELKIND_RELATION)
      {
            /* toast table entries should never be recursively toasted */
            Assert(!HeapTupleHasExternal(tup));
            heaptup = tup;
      }
      else if (HeapTupleHasExternal(tup) || tup->t_len > TOAST_TUPLE_THRESHOLD)
            heaptup = toast_insert_or_update(relation, tup, NULL, options);
      else
            heaptup = tup;

      /* Find buffer to insert this tuple into */
      buffer = RelationGetBufferForTuple(relation, heaptup->t_len,
                                                         InvalidBuffer, options, bistate);

      /* NO EREPORT(ERROR) from here till changes are logged */
      START_CRIT_SECTION();

      RelationPutHeapTuple(relation, buffer, heaptup);

      if (PageIsAllVisible(BufferGetPage(buffer)))
      {
            all_visible_cleared = true;
            PageClearAllVisible(BufferGetPage(buffer));
      }

      /*
       * XXX Should we set PageSetPrunable on this page ?
       *
       * The inserting transaction may eventually abort thus making this tuple
       * DEAD and hence available for pruning. Though we don't want to optimize
       * for aborts, if no other tuple in this page is UPDATEd/DELETEd, the
       * aborted tuple will never be pruned until next vacuum is triggered.
       *
       * If you do add PageSetPrunable here, add it in heap_xlog_insert too.
       */

      MarkBufferDirty(buffer);

      /* XLOG stuff */
      if (!(options & HEAP_INSERT_SKIP_WAL) && !relation->rd_istemp)
      {
            xl_heap_insert xlrec;
            xl_heap_header xlhdr;
            XLogRecPtr  recptr;
            XLogRecData rdata[3];
            Page        page = BufferGetPage(buffer);
            uint8       info = XLOG_HEAP_INSERT;

            xlrec.all_visible_cleared = all_visible_cleared;
            xlrec.target.node = relation->rd_node;
            xlrec.target.tid = heaptup->t_self;
            rdata[0].data = (char *) &xlrec;
            rdata[0].len = SizeOfHeapInsert;
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &(rdata[1]);

            xlhdr.t_infomask2 = heaptup->t_data->t_infomask2;
            xlhdr.t_infomask = heaptup->t_data->t_infomask;
            xlhdr.t_hoff = heaptup->t_data->t_hoff;

            /*
             * note we mark rdata[1] as belonging to buffer; if XLogInsert decides
             * to write the whole page to the xlog, we don't need to store
             * xl_heap_header in the xlog.
             */
            rdata[1].data = (char *) &xlhdr;
            rdata[1].len = SizeOfHeapHeader;
            rdata[1].buffer = buffer;
            rdata[1].buffer_std = true;
            rdata[1].next = &(rdata[2]);

            /* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
            rdata[2].data = (char *) heaptup->t_data + offsetof(HeapTupleHeaderData, t_bits);
            rdata[2].len = heaptup->t_len - offsetof(HeapTupleHeaderData, t_bits);
            rdata[2].buffer = buffer;
            rdata[2].buffer_std = true;
            rdata[2].next = NULL;

            /*
             * If this is the single and first tuple on page, we can reinit the
             * page instead of restoring the whole thing.  Set flag, and hide
             * buffer references from XLogInsert.
             */
            if (ItemPointerGetOffsetNumber(&(heaptup->t_self)) == FirstOffsetNumber &&
                  PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
            {
                  info |= XLOG_HEAP_INIT_PAGE;
                  rdata[1].buffer = rdata[2].buffer = InvalidBuffer;
            }

            recptr = XLogInsert(RM_HEAP_ID, info, rdata);

            PageSetLSN(page, recptr);
            PageSetTLI(page, ThisTimeLineID);
      }

      END_CRIT_SECTION();

      UnlockReleaseBuffer(buffer);

      /* Clear the bit in the visibility map if necessary */
      if (all_visible_cleared)
            visibilitymap_clear(relation,
                                          ItemPointerGetBlockNumber(&(heaptup->t_self)));

      /*
       * If tuple is cachable, mark it for invalidation from the caches in case
       * we abort.  Note it is OK to do this after releasing the buffer, because
       * the heaptup data structure is all in local memory, not in the shared
       * buffer.
       */
      CacheInvalidateHeapTuple(relation, heaptup);

      pgstat_count_heap_insert(relation);

      /*
       * If heaptup is a private copy, release it.  Don't forget to copy t_self
       * back to the caller's image, too.
       */
      if (heaptup != tup)
      {
            tup->t_self = heaptup->t_self;
            heap_freetuple(heaptup);
      }

      return HeapTupleGetOid(tup);
}

/*
 *    simple_heap_insert - insert a tuple
 *
 * Currently, this routine differs from heap_insert only in supplying
 * a default command ID and not allowing access to the speedup options.
 *
 * This should be used rather than using heap_insert directly in most places
 * where we are modifying system catalogs.
 */
Oid
simple_heap_insert(Relation relation, HeapTuple tup)
{
      return heap_insert(relation, tup, GetCurrentCommandId(true), 0, NULL);
}

/*
 *    heap_delete - delete a tuple
 *
 * NB: do not call this directly unless you are prepared to deal with
 * concurrent-update conditions.  Use simple_heap_delete instead.
 *
 *    relation - table to be modified (caller must hold suitable lock)
 *    tid - TID of tuple to be deleted
 *    ctid - output parameter, used only for failure case (see below)
 *    update_xmax - output parameter, used only for failure case (see below)
 *    cid - delete command ID (used for visibility test, and stored into
 *          cmax if successful)
 *    crosscheck - if not InvalidSnapshot, also check tuple against this
 *    wait - true if should wait for any conflicting update to commit/abort
 *
 * Normal, successful return value is HeapTupleMayBeUpdated, which
 * actually means we did delete it.  Failure return codes are
 * HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
 * (the last only possible if wait == false).
 *
 * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
 * If t_ctid is the same as tid, the tuple was deleted; if different, the
 * tuple was updated, and t_ctid is the location of the replacement tuple.
 * (t_xmax is needed to verify that the replacement tuple matches.)
 */
HTSU_Result
heap_delete(Relation relation, ItemPointer tid,
                  ItemPointer ctid, TransactionId *update_xmax,
                  CommandId cid, Snapshot crosscheck, bool wait)
{
      HTSU_Result result;
      TransactionId xid = GetCurrentTransactionId();
      ItemId            lp;
      HeapTupleData tp;
      Page        page;
      Buffer            buffer;
      bool        have_tuple_lock = false;
      bool        iscombo;
      bool        all_visible_cleared = false;

      Assert(ItemPointerIsValid(tid));

      buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
      LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

      page = BufferGetPage(buffer);
      lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
      Assert(ItemIdIsNormal(lp));

      tp.t_data = (HeapTupleHeader) PageGetItem(page, lp);
      tp.t_len = ItemIdGetLength(lp);
      tp.t_self = *tid;

l1:
      result = HeapTupleSatisfiesUpdate(tp.t_data, cid, buffer);

      if (result == HeapTupleInvisible)
      {
            UnlockReleaseBuffer(buffer);
            elog(ERROR, "attempted to delete invisible tuple");
      }
      else if (result == HeapTupleBeingUpdated && wait)
      {
            TransactionId xwait;
            uint16            infomask;

            /* must copy state data before unlocking buffer */
            xwait = HeapTupleHeaderGetXmax(tp.t_data);
            infomask = tp.t_data->t_infomask;

            LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

            /*
             * Acquire tuple lock to establish our priority for the tuple (see
             * heap_lock_tuple).  LockTuple will release us when we are
             * next-in-line for the tuple.
             *
             * If we are forced to "start over" below, we keep the tuple lock;
             * this arranges that we stay at the head of the line while rechecking
             * tuple state.
             */
            if (!have_tuple_lock)
            {
                  LockTuple(relation, &(tp.t_self), ExclusiveLock);
                  have_tuple_lock = true;
            }

            /*
             * Sleep until concurrent transaction ends.  Note that we don't care
             * if the locker has an exclusive or shared lock, because we need
             * exclusive.
             */

            if (infomask & HEAP_XMAX_IS_MULTI)
            {
                  /* wait for multixact */
                  MultiXactIdWait((MultiXactId) xwait);
                  LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

                  /*
                   * If xwait had just locked the tuple then some other xact could
                   * update this tuple before we get to this point.  Check for xmax
                   * change, and start over if so.
                   */
                  if (!(tp.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
                        !TransactionIdEquals(HeapTupleHeaderGetXmax(tp.t_data),
                                                       xwait))
                        goto l1;

                  /*
                   * You might think the multixact is necessarily done here, but not
                   * so: it could have surviving members, namely our own xact or
                   * other subxacts of this backend.  It is legal for us to delete
                   * the tuple in either case, however (the latter case is
                   * essentially a situation of upgrading our former shared lock to
                   * exclusive).    We don't bother changing the on-disk hint bits
                   * since we are about to overwrite the xmax altogether.
                   */
            }
            else
            {
                  /* wait for regular transaction to end */
                  XactLockTableWait(xwait);
                  LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

                  /*
                   * xwait is done, but if xwait had just locked the tuple then some
                   * other xact could update this tuple before we get to this point.
                   * Check for xmax change, and start over if so.
                   */
                  if ((tp.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
                        !TransactionIdEquals(HeapTupleHeaderGetXmax(tp.t_data),
                                                       xwait))
                        goto l1;

                  /* Otherwise check if it committed or aborted */
                  UpdateXmaxHintBits(tp.t_data, buffer, xwait);
            }

            /*
             * We may overwrite if previous xmax aborted, or if it committed but
             * only locked the tuple without updating it.
             */
            if (tp.t_data->t_infomask & (HEAP_XMAX_INVALID |
                                                       HEAP_IS_LOCKED))
                  result = HeapTupleMayBeUpdated;
            else
                  result = HeapTupleUpdated;
      }

      if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
      {
            /* Perform additional check for serializable RI updates */
            if (!HeapTupleSatisfiesVisibility(&tp, crosscheck, buffer))
                  result = HeapTupleUpdated;
      }

      if (result != HeapTupleMayBeUpdated)
      {
            Assert(result == HeapTupleSelfUpdated ||
                     result == HeapTupleUpdated ||
                     result == HeapTupleBeingUpdated);
            Assert(!(tp.t_data->t_infomask & HEAP_XMAX_INVALID));
            *ctid = tp.t_data->t_ctid;
            *update_xmax = HeapTupleHeaderGetXmax(tp.t_data);
            UnlockReleaseBuffer(buffer);
            if (have_tuple_lock)
                  UnlockTuple(relation, &(tp.t_self), ExclusiveLock);
            return result;
      }

      /* replace cid with a combo cid if necessary */
      HeapTupleHeaderAdjustCmax(tp.t_data, &cid, &iscombo);

      START_CRIT_SECTION();

      /*
       * If this transaction commits, the tuple will become DEAD sooner or
       * later.  Set flag that this page is a candidate for pruning once our xid
       * falls below the OldestXmin horizon.    If the transaction finally aborts,
       * the subsequent page pruning will be a no-op and the hint will be
       * cleared.
       */
      PageSetPrunable(page, xid);

      if (PageIsAllVisible(page))
      {
            all_visible_cleared = true;
            PageClearAllVisible(page);
      }

      /* store transaction information of xact deleting the tuple */
      tp.t_data->t_infomask &= ~(HEAP_XMAX_COMMITTED |
                                             HEAP_XMAX_INVALID |
                                             HEAP_XMAX_IS_MULTI |
                                             HEAP_IS_LOCKED |
                                             HEAP_MOVED);
      HeapTupleHeaderClearHotUpdated(tp.t_data);
      HeapTupleHeaderSetXmax(tp.t_data, xid);
      HeapTupleHeaderSetCmax(tp.t_data, cid, iscombo);
      /* Make sure there is no forward chain link in t_ctid */
      tp.t_data->t_ctid = tp.t_self;

      MarkBufferDirty(buffer);

      /* XLOG stuff */
      if (!relation->rd_istemp)
      {
            xl_heap_delete xlrec;
            XLogRecPtr  recptr;
            XLogRecData rdata[2];

            xlrec.all_visible_cleared = all_visible_cleared;
            xlrec.target.node = relation->rd_node;
            xlrec.target.tid = tp.t_self;
            rdata[0].data = (char *) &xlrec;
            rdata[0].len = SizeOfHeapDelete;
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &(rdata[1]);

            rdata[1].data = NULL;
            rdata[1].len = 0;
            rdata[1].buffer = buffer;
            rdata[1].buffer_std = true;
            rdata[1].next = NULL;

            recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_DELETE, rdata);

            PageSetLSN(page, recptr);
            PageSetTLI(page, ThisTimeLineID);
      }

      END_CRIT_SECTION();

      LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

      /*
       * If the tuple has toasted out-of-line attributes, we need to delete
       * those items too.  We have to do this before releasing the buffer
       * because we need to look at the contents of the tuple, but it's OK to
       * release the content lock on the buffer first.
       */
      if (relation->rd_rel->relkind != RELKIND_RELATION)
      {
            /* toast table entries should never be recursively toasted */
            Assert(!HeapTupleHasExternal(&tp));
      }
      else if (HeapTupleHasExternal(&tp))
            toast_delete(relation, &tp);

      /*
       * Mark tuple for invalidation from system caches at next command
       * boundary. We have to do this before releasing the buffer because we
       * need to look at the contents of the tuple.
       */
      CacheInvalidateHeapTuple(relation, &tp);

      /* Clear the bit in the visibility map if necessary */
      if (all_visible_cleared)
            visibilitymap_clear(relation, BufferGetBlockNumber(buffer));

      /* Now we can release the buffer */
      ReleaseBuffer(buffer);

      /*
       * Release the lmgr tuple lock, if we had it.
       */
      if (have_tuple_lock)
            UnlockTuple(relation, &(tp.t_self), ExclusiveLock);

      pgstat_count_heap_delete(relation);

      return HeapTupleMayBeUpdated;
}

/*
 *    simple_heap_delete - delete a tuple
 *
 * This routine may be used to delete a tuple when concurrent updates of
 * the target tuple are not expected (for example, because we have a lock
 * on the relation associated with the tuple).  Any failure is reported
 * via ereport().
 */
void
simple_heap_delete(Relation relation, ItemPointer tid)
{
      HTSU_Result result;
      ItemPointerData update_ctid;
      TransactionId update_xmax;

      result = heap_delete(relation, tid,
                                     &update_ctid, &update_xmax,
                                     GetCurrentCommandId(true), InvalidSnapshot,
                                     true /* wait for commit */ );
      switch (result)
      {
            case HeapTupleSelfUpdated:
                  /* Tuple was already updated in current command? */
                  elog(ERROR, "tuple already updated by self");
                  break;

            case HeapTupleMayBeUpdated:
                  /* done successfully */
                  break;

            case HeapTupleUpdated:
                  elog(ERROR, "tuple concurrently updated");
                  break;

            default:
                  elog(ERROR, "unrecognized heap_delete status: %u", result);
                  break;
      }
}

/*
 *    heap_update - replace a tuple
 *
 * NB: do not call this directly unless you are prepared to deal with
 * concurrent-update conditions.  Use simple_heap_update instead.
 *
 *    relation - table to be modified (caller must hold suitable lock)
 *    otid - TID of old tuple to be replaced
 *    newtup - newly constructed tuple data to store
 *    ctid - output parameter, used only for failure case (see below)
 *    update_xmax - output parameter, used only for failure case (see below)
 *    cid - update command ID (used for visibility test, and stored into
 *          cmax/cmin if successful)
 *    crosscheck - if not InvalidSnapshot, also check old tuple against this
 *    wait - true if should wait for any conflicting update to commit/abort
 *
 * Normal, successful return value is HeapTupleMayBeUpdated, which
 * actually means we *did* update it.  Failure return codes are
 * HeapTupleSelfUpdated, HeapTupleUpdated, or HeapTupleBeingUpdated
 * (the last only possible if wait == false).
 *
 * On success, the header fields of *newtup are updated to match the new
 * stored tuple; in particular, newtup->t_self is set to the TID where the
 * new tuple was inserted, and its HEAP_ONLY_TUPLE flag is set iff a HOT
 * update was done.  However, any TOAST changes in the new tuple's
 * data are not reflected into *newtup.
 *
 * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
 * If t_ctid is the same as otid, the tuple was deleted; if different, the
 * tuple was updated, and t_ctid is the location of the replacement tuple.
 * (t_xmax is needed to verify that the replacement tuple matches.)
 */
HTSU_Result
heap_update(Relation relation, ItemPointer otid, HeapTuple newtup,
                  ItemPointer ctid, TransactionId *update_xmax,
                  CommandId cid, Snapshot crosscheck, bool wait)
{
      HTSU_Result result;
      TransactionId xid = GetCurrentTransactionId();
      Bitmapset  *hot_attrs;
      ItemId            lp;
      HeapTupleData oldtup;
      HeapTuple   heaptup;
      Page        page;
      Buffer            buffer,
                        newbuf;
      bool        need_toast,
                        already_marked;
      Size        newtupsize,
                        pagefree;
      bool        have_tuple_lock = false;
      bool        iscombo;
      bool        use_hot_update = false;
      bool        all_visible_cleared = false;
      bool        all_visible_cleared_new = false;

      Assert(ItemPointerIsValid(otid));

      /*
       * Fetch the list of attributes to be checked for HOT update.  This is
       * wasted effort if we fail to update or have to put the new tuple on a
       * different page.      But we must compute the list before obtaining buffer
       * lock --- in the worst case, if we are doing an update on one of the
       * relevant system catalogs, we could deadlock if we try to fetch the list
       * later.  In any case, the relcache caches the data so this is usually
       * pretty cheap.
       *
       * Note that we get a copy here, so we need not worry about relcache flush
       * happening midway through.
       */
      hot_attrs = RelationGetIndexAttrBitmap(relation);

      buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(otid));
      LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

      page = BufferGetPage(buffer);
      lp = PageGetItemId(page, ItemPointerGetOffsetNumber(otid));
      Assert(ItemIdIsNormal(lp));

      oldtup.t_data = (HeapTupleHeader) PageGetItem(page, lp);
      oldtup.t_len = ItemIdGetLength(lp);
      oldtup.t_self = *otid;

      /*
       * Note: beyond this point, use oldtup not otid to refer to old tuple.
       * otid may very well point at newtup->t_self, which we will overwrite
       * with the new tuple's location, so there's great risk of confusion if we
       * use otid anymore.
       */

l2:
      result = HeapTupleSatisfiesUpdate(oldtup.t_data, cid, buffer);

      if (result == HeapTupleInvisible)
      {
            UnlockReleaseBuffer(buffer);
            elog(ERROR, "attempted to update invisible tuple");
      }
      else if (result == HeapTupleBeingUpdated && wait)
      {
            TransactionId xwait;
            uint16            infomask;

            /* must copy state data before unlocking buffer */
            xwait = HeapTupleHeaderGetXmax(oldtup.t_data);
            infomask = oldtup.t_data->t_infomask;

            LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

            /*
             * Acquire tuple lock to establish our priority for the tuple (see
             * heap_lock_tuple).  LockTuple will release us when we are
             * next-in-line for the tuple.
             *
             * If we are forced to "start over" below, we keep the tuple lock;
             * this arranges that we stay at the head of the line while rechecking
             * tuple state.
             */
            if (!have_tuple_lock)
            {
                  LockTuple(relation, &(oldtup.t_self), ExclusiveLock);
                  have_tuple_lock = true;
            }

            /*
             * Sleep until concurrent transaction ends.  Note that we don't care
             * if the locker has an exclusive or shared lock, because we need
             * exclusive.
             */

            if (infomask & HEAP_XMAX_IS_MULTI)
            {
                  /* wait for multixact */
                  MultiXactIdWait((MultiXactId) xwait);
                  LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

                  /*
                   * If xwait had just locked the tuple then some other xact could
                   * update this tuple before we get to this point.  Check for xmax
                   * change, and start over if so.
                   */
                  if (!(oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
                        !TransactionIdEquals(HeapTupleHeaderGetXmax(oldtup.t_data),
                                                       xwait))
                        goto l2;

                  /*
                   * You might think the multixact is necessarily done here, but not
                   * so: it could have surviving members, namely our own xact or
                   * other subxacts of this backend.  It is legal for us to update
                   * the tuple in either case, however (the latter case is
                   * essentially a situation of upgrading our former shared lock to
                   * exclusive).    We don't bother changing the on-disk hint bits
                   * since we are about to overwrite the xmax altogether.
                   */
            }
            else
            {
                  /* wait for regular transaction to end */
                  XactLockTableWait(xwait);
                  LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);

                  /*
                   * xwait is done, but if xwait had just locked the tuple then some
                   * other xact could update this tuple before we get to this point.
                   * Check for xmax change, and start over if so.
                   */
                  if ((oldtup.t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
                        !TransactionIdEquals(HeapTupleHeaderGetXmax(oldtup.t_data),
                                                       xwait))
                        goto l2;

                  /* Otherwise check if it committed or aborted */
                  UpdateXmaxHintBits(oldtup.t_data, buffer, xwait);
            }

            /*
             * We may overwrite if previous xmax aborted, or if it committed but
             * only locked the tuple without updating it.
             */
            if (oldtup.t_data->t_infomask & (HEAP_XMAX_INVALID |
                                                             HEAP_IS_LOCKED))
                  result = HeapTupleMayBeUpdated;
            else
                  result = HeapTupleUpdated;
      }

      if (crosscheck != InvalidSnapshot && result == HeapTupleMayBeUpdated)
      {
            /* Perform additional check for serializable RI updates */
            if (!HeapTupleSatisfiesVisibility(&oldtup, crosscheck, buffer))
                  result = HeapTupleUpdated;
      }

      if (result != HeapTupleMayBeUpdated)
      {
            Assert(result == HeapTupleSelfUpdated ||
                     result == HeapTupleUpdated ||
                     result == HeapTupleBeingUpdated);
            Assert(!(oldtup.t_data->t_infomask & HEAP_XMAX_INVALID));
            *ctid = oldtup.t_data->t_ctid;
            *update_xmax = HeapTupleHeaderGetXmax(oldtup.t_data);
            UnlockReleaseBuffer(buffer);
            if (have_tuple_lock)
                  UnlockTuple(relation, &(oldtup.t_self), ExclusiveLock);
            bms_free(hot_attrs);
            return result;
      }

      /* Fill in OID and transaction status data for newtup */
      if (relation->rd_rel->relhasoids)
      {
#ifdef NOT_USED
            /* this is redundant with an Assert in HeapTupleSetOid */
            Assert(newtup->t_data->t_infomask & HEAP_HASOID);
#endif
            HeapTupleSetOid(newtup, HeapTupleGetOid(&oldtup));
      }
      else
      {
            /* check there is not space for an OID */
            Assert(!(newtup->t_data->t_infomask & HEAP_HASOID));
      }

      newtup->t_data->t_infomask &= ~(HEAP_XACT_MASK);
      newtup->t_data->t_infomask2 &= ~(HEAP2_XACT_MASK);
      newtup->t_data->t_infomask |= (HEAP_XMAX_INVALID | HEAP_UPDATED);
      HeapTupleHeaderSetXmin(newtup->t_data, xid);
      HeapTupleHeaderSetCmin(newtup->t_data, cid);
      HeapTupleHeaderSetXmax(newtup->t_data, 0);      /* for cleanliness */
      newtup->t_tableOid = RelationGetRelid(relation);

      /*
       * Replace cid with a combo cid if necessary.  Note that we already put
       * the plain cid into the new tuple.
       */
      HeapTupleHeaderAdjustCmax(oldtup.t_data, &cid, &iscombo);

      /*
       * If the toaster needs to be activated, OR if the new tuple will not fit
       * on the same page as the old, then we need to release the content lock
       * (but not the pin!) on the old tuple's buffer while we are off doing
       * TOAST and/or table-file-extension work.      We must mark the old tuple to
       * show that it's already being updated, else other processes may try to
       * update it themselves.
       *
       * We need to invoke the toaster if there are already any out-of-line
       * toasted values present, or if the new tuple is over-threshold.
       */
      if (relation->rd_rel->relkind != RELKIND_RELATION)
      {
            /* toast table entries should never be recursively toasted */
            Assert(!HeapTupleHasExternal(&oldtup));
            Assert(!HeapTupleHasExternal(newtup));
            need_toast = false;
      }
      else
            need_toast = (HeapTupleHasExternal(&oldtup) ||
                                HeapTupleHasExternal(newtup) ||
                                newtup->t_len > TOAST_TUPLE_THRESHOLD);

      pagefree = PageGetHeapFreeSpace(page);

      newtupsize = MAXALIGN(newtup->t_len);

      if (need_toast || newtupsize > pagefree)
      {
            /* Clear obsolete visibility flags ... */
            oldtup.t_data->t_infomask &= ~(HEAP_XMAX_COMMITTED |
                                                         HEAP_XMAX_INVALID |
                                                         HEAP_XMAX_IS_MULTI |
                                                         HEAP_IS_LOCKED |
                                                         HEAP_MOVED);
            HeapTupleClearHotUpdated(&oldtup);
            /* ... and store info about transaction updating this tuple */
            HeapTupleHeaderSetXmax(oldtup.t_data, xid);
            HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
            /* temporarily make it look not-updated */
            oldtup.t_data->t_ctid = oldtup.t_self;
            already_marked = true;
            LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

            /*
             * Let the toaster do its thing, if needed.
             *
             * Note: below this point, heaptup is the data we actually intend to
             * store into the relation; newtup is the caller's original untoasted
             * data.
             */
            if (need_toast)
            {
                  /* Note we always use WAL and FSM during updates */
                  heaptup = toast_insert_or_update(relation, newtup, &oldtup, 0);
                  newtupsize = MAXALIGN(heaptup->t_len);
            }
            else
                  heaptup = newtup;

            /*
             * Now, do we need a new page for the tuple, or not?  This is a bit
             * tricky since someone else could have added tuples to the page while
             * we weren't looking.  We have to recheck the available space after
             * reacquiring the buffer lock.  But don't bother to do that if the
             * former amount of free space is still not enough; it's unlikely
             * there's more free now than before.
             *
             * What's more, if we need to get a new page, we will need to acquire
             * buffer locks on both old and new pages.      To avoid deadlock against
             * some other backend trying to get the same two locks in the other
             * order, we must be consistent about the order we get the locks in.
             * We use the rule "lock the lower-numbered page of the relation
             * first".  To implement this, we must do RelationGetBufferForTuple
             * while not holding the lock on the old page, and we must rely on it
             * to get the locks on both pages in the correct order.
             */
            if (newtupsize > pagefree)
            {
                  /* Assume there's no chance to put heaptup on same page. */
                  newbuf = RelationGetBufferForTuple(relation, heaptup->t_len,
                                                                     buffer, 0, NULL);
            }
            else
            {
                  /* Re-acquire the lock on the old tuple's page. */
                  LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
                  /* Re-check using the up-to-date free space */
                  pagefree = PageGetHeapFreeSpace(page);
                  if (newtupsize > pagefree)
                  {
                        /*
                         * Rats, it doesn't fit anymore.  We must now unlock and
                         * relock to avoid deadlock.  Fortunately, this path should
                         * seldom be taken.
                         */
                        LockBuffer(buffer, BUFFER_LOCK_UNLOCK);
                        newbuf = RelationGetBufferForTuple(relation, heaptup->t_len,
                                                                           buffer, 0, NULL);
                  }
                  else
                  {
                        /* OK, it fits here, so we're done. */
                        newbuf = buffer;
                  }
            }
      }
      else
      {
            /* No TOAST work needed, and it'll fit on same page */
            already_marked = false;
            newbuf = buffer;
            heaptup = newtup;
      }

      /*
       * At this point newbuf and buffer are both pinned and locked, and newbuf
       * has enough space for the new tuple.    If they are the same buffer, only
       * one pin is held.
       */

      if (newbuf == buffer)
      {
            /*
             * Since the new tuple is going into the same page, we might be able
             * to do a HOT update.  Check if any of the index columns have been
             * changed.  If not, then HOT update is possible.
             */
            if (HeapSatisfiesHOTUpdate(relation, hot_attrs, &oldtup, heaptup))
                  use_hot_update = true;
      }
      else
      {
            /* Set a hint that the old page could use prune/defrag */
            PageSetFull(page);
      }

      /* NO EREPORT(ERROR) from here till changes are logged */
      START_CRIT_SECTION();

      /*
       * If this transaction commits, the old tuple will become DEAD sooner or
       * later.  Set flag that this page is a candidate for pruning once our xid
       * falls below the OldestXmin horizon.    If the transaction finally aborts,
       * the subsequent page pruning will be a no-op and the hint will be
       * cleared.
       *
       * XXX Should we set hint on newbuf as well?  If the transaction aborts,
       * there would be a prunable tuple in the newbuf; but for now we choose
       * not to optimize for aborts.      Note that heap_xlog_update must be kept in
       * sync if this decision changes.
       */
      PageSetPrunable(page, xid);

      if (use_hot_update)
      {
            /* Mark the old tuple as HOT-updated */
            HeapTupleSetHotUpdated(&oldtup);
            /* And mark the new tuple as heap-only */
            HeapTupleSetHeapOnly(heaptup);
            /* Mark the caller's copy too, in case different from heaptup */
            HeapTupleSetHeapOnly(newtup);
      }
      else
      {
            /* Make sure tuples are correctly marked as not-HOT */
            HeapTupleClearHotUpdated(&oldtup);
            HeapTupleClearHeapOnly(heaptup);
            HeapTupleClearHeapOnly(newtup);
      }

      RelationPutHeapTuple(relation, newbuf, heaptup);      /* insert new tuple */

      if (!already_marked)
      {
            /* Clear obsolete visibility flags ... */
            oldtup.t_data->t_infomask &= ~(HEAP_XMAX_COMMITTED |
                                                         HEAP_XMAX_INVALID |
                                                         HEAP_XMAX_IS_MULTI |
                                                         HEAP_IS_LOCKED |
                                                         HEAP_MOVED);
            /* ... and store info about transaction updating this tuple */
            HeapTupleHeaderSetXmax(oldtup.t_data, xid);
            HeapTupleHeaderSetCmax(oldtup.t_data, cid, iscombo);
      }

      /* record address of new tuple in t_ctid of old one */
      oldtup.t_data->t_ctid = heaptup->t_self;

      if (newbuf != buffer)
            MarkBufferDirty(newbuf);
      MarkBufferDirty(buffer);

      /*
       * Note: we mustn't clear PD_ALL_VISIBLE flags before writing the WAL
       * record, because log_heap_update looks at those flags to set the
       * corresponding flags in the WAL record.
       */

      /* XLOG stuff */
      if (!relation->rd_istemp)
      {
            XLogRecPtr  recptr = log_heap_update(relation, buffer, oldtup.t_self,
                                                                   newbuf, heaptup, false);

            if (newbuf != buffer)
            {
                  PageSetLSN(BufferGetPage(newbuf), recptr);
                  PageSetTLI(BufferGetPage(newbuf), ThisTimeLineID);
            }
            PageSetLSN(BufferGetPage(buffer), recptr);
            PageSetTLI(BufferGetPage(buffer), ThisTimeLineID);
      }

      /* Clear PD_ALL_VISIBLE flags */
      if (PageIsAllVisible(BufferGetPage(buffer)))
      {
            all_visible_cleared = true;
            PageClearAllVisible(BufferGetPage(buffer));
      }
      if (newbuf != buffer && PageIsAllVisible(BufferGetPage(newbuf)))
      {
            all_visible_cleared_new = true;
            PageClearAllVisible(BufferGetPage(newbuf));
      }

      END_CRIT_SECTION();

      if (newbuf != buffer)
            LockBuffer(newbuf, BUFFER_LOCK_UNLOCK);
      LockBuffer(buffer, BUFFER_LOCK_UNLOCK);

      /*
       * Mark old tuple for invalidation from system caches at next command
       * boundary. We have to do this before releasing the buffer because we
       * need to look at the contents of the tuple.
       */
      CacheInvalidateHeapTuple(relation, &oldtup);

      /* Clear bits in visibility map */
      if (all_visible_cleared)
            visibilitymap_clear(relation, BufferGetBlockNumber(buffer));
      if (all_visible_cleared_new)
            visibilitymap_clear(relation, BufferGetBlockNumber(newbuf));

      /* Now we can release the buffer(s) */
      if (newbuf != buffer)
            ReleaseBuffer(newbuf);
      ReleaseBuffer(buffer);

      /*
       * If new tuple is cachable, mark it for invalidation from the caches in
       * case we abort.  Note it is OK to do this after releasing the buffer,
       * because the heaptup data structure is all in local memory, not in the
       * shared buffer.
       */
      CacheInvalidateHeapTuple(relation, heaptup);

      /*
       * Release the lmgr tuple lock, if we had it.
       */
      if (have_tuple_lock)
            UnlockTuple(relation, &(oldtup.t_self), ExclusiveLock);

      pgstat_count_heap_update(relation, use_hot_update);

      /*
       * If heaptup is a private copy, release it.  Don't forget to copy t_self
       * back to the caller's image, too.
       */
      if (heaptup != newtup)
      {
            newtup->t_self = heaptup->t_self;
            heap_freetuple(heaptup);
      }

      bms_free(hot_attrs);

      return HeapTupleMayBeUpdated;
}

/*
 * Check if the specified attribute's value is same in both given tuples.
 * Subroutine for HeapSatisfiesHOTUpdate.
 */
static bool
heap_tuple_attr_equals(TupleDesc tupdesc, int attrnum,
                                 HeapTuple tup1, HeapTuple tup2)
{
      Datum       value1,
                        value2;
      bool        isnull1,
                        isnull2;
      Form_pg_attribute att;

      /*
       * If it's a whole-tuple reference, say "not equal".  It's not really
       * worth supporting this case, since it could only succeed after a no-op
       * update, which is hardly a case worth optimizing for.
       */
      if (attrnum == 0)
            return false;

      /*
       * Likewise, automatically say "not equal" for any system attribute other
       * than OID and tableOID; we cannot expect these to be consistent in a HOT
       * chain, or even to be set correctly yet in the new tuple.
       */
      if (attrnum < 0)
      {
            if (attrnum != ObjectIdAttributeNumber &&
                  attrnum != TableOidAttributeNumber)
                  return false;
      }

      /*
       * Extract the corresponding values.  XXX this is pretty inefficient if
       * there are many indexed columns.  Should HeapSatisfiesHOTUpdate do a
       * single heap_deform_tuple call on each tuple, instead?  But that doesn't
       * work for system columns ...
       */
      value1 = heap_getattr(tup1, attrnum, tupdesc, &isnull1);
      value2 = heap_getattr(tup2, attrnum, tupdesc, &isnull2);

      /*
       * If one value is NULL and other is not, then they are certainly not
       * equal
       */
      if (isnull1 != isnull2)
            return false;

      /*
       * If both are NULL, they can be considered equal.
       */
      if (isnull1)
            return true;

      /*
       * We do simple binary comparison of the two datums.  This may be overly
       * strict because there can be multiple binary representations for the
       * same logical value.  But we should be OK as long as there are no false
       * positives.  Using a type-specific equality operator is messy because
       * there could be multiple notions of equality in different operator
       * classes; furthermore, we cannot safely invoke user-defined functions
       * while holding exclusive buffer lock.
       */
      if (attrnum <= 0)
      {
            /* The only allowed system columns are OIDs, so do this */
            return (DatumGetObjectId(value1) == DatumGetObjectId(value2));
      }
      else
      {
            Assert(attrnum <= tupdesc->natts);
            att = tupdesc->attrs[attrnum - 1];
            return datumIsEqual(value1, value2, att->attbyval, att->attlen);
      }
}

/*
 * Check if the old and new tuples represent a HOT-safe update. To be able
 * to do a HOT update, we must not have changed any columns used in index
 * definitions.
 *
 * The set of attributes to be checked is passed in (we dare not try to
 * compute it while holding exclusive buffer lock...)  NOTE that hot_attrs
 * is destructively modified!  That is OK since this is invoked at most once
 * by heap_update().
 *
 * Returns true if safe to do HOT update.
 */
static bool
HeapSatisfiesHOTUpdate(Relation relation, Bitmapset *hot_attrs,
                                 HeapTuple oldtup, HeapTuple newtup)
{
      int               attrnum;

      while ((attrnum = bms_first_member(hot_attrs)) >= 0)
      {
            /* Adjust for system attributes */
            attrnum += FirstLowInvalidHeapAttributeNumber;

            /* If the attribute value has changed, we can't do HOT update */
            if (!heap_tuple_attr_equals(RelationGetDescr(relation), attrnum,
                                                      oldtup, newtup))
                  return false;
      }

      return true;
}

/*
 *    simple_heap_update - replace a tuple
 *
 * This routine may be used to update a tuple when concurrent updates of
 * the target tuple are not expected (for example, because we have a lock
 * on the relation associated with the tuple).  Any failure is reported
 * via ereport().
 */
void
simple_heap_update(Relation relation, ItemPointer otid, HeapTuple tup)
{
      HTSU_Result result;
      ItemPointerData update_ctid;
      TransactionId update_xmax;

      result = heap_update(relation, otid, tup,
                                     &update_ctid, &update_xmax,
                                     GetCurrentCommandId(true), InvalidSnapshot,
                                     true /* wait for commit */ );
      switch (result)
      {
            case HeapTupleSelfUpdated:
                  /* Tuple was already updated in current command? */
                  elog(ERROR, "tuple already updated by self");
                  break;

            case HeapTupleMayBeUpdated:
                  /* done successfully */
                  break;

            case HeapTupleUpdated:
                  elog(ERROR, "tuple concurrently updated");
                  break;

            default:
                  elog(ERROR, "unrecognized heap_update status: %u", result);
                  break;
      }
}

/*
 *    heap_lock_tuple - lock a tuple in shared or exclusive mode
 *
 * Note that this acquires a buffer pin, which the caller must release.
 *
 * Input parameters:
 *    relation: relation containing tuple (caller must hold suitable lock)
 *    tuple->t_self: TID of tuple to lock (rest of struct need not be valid)
 *    cid: current command ID (used for visibility test, and stored into
 *          tuple's cmax if lock is successful)
 *    mode: indicates if shared or exclusive tuple lock is desired
 *    nowait: if true, ereport rather than blocking if lock not available
 *
 * Output parameters:
 *    *tuple: all fields filled in
 *    *buffer: set to buffer holding tuple (pinned but not locked at exit)
 *    *ctid: set to tuple's t_ctid, but only in failure cases
 *    *update_xmax: set to tuple's xmax, but only in failure cases
 *
 * Function result may be:
 *    HeapTupleMayBeUpdated: lock was successfully acquired
 *    HeapTupleSelfUpdated: lock failed because tuple updated by self
 *    HeapTupleUpdated: lock failed because tuple updated by other xact
 *
 * In the failure cases, the routine returns the tuple's t_ctid and t_xmax.
 * If t_ctid is the same as t_self, the tuple was deleted; if different, the
 * tuple was updated, and t_ctid is the location of the replacement tuple.
 * (t_xmax is needed to verify that the replacement tuple matches.)
 *
 *
 * NOTES: because the shared-memory lock table is of finite size, but users
 * could reasonably want to lock large numbers of tuples, we do not rely on
 * the standard lock manager to store tuple-level locks over the long term.
 * Instead, a tuple is marked as locked by setting the current transaction's
 * XID as its XMAX, and setting additional infomask bits to distinguish this
 * usage from the more normal case of having deleted the tuple.  When
 * multiple transactions concurrently share-lock a tuple, the first locker's
 * XID is replaced in XMAX with a MultiTransactionId representing the set of
 * XIDs currently holding share-locks.
 *
 * When it is necessary to wait for a tuple-level lock to be released, the
 * basic delay is provided by XactLockTableWait or MultiXactIdWait on the
 * contents of the tuple's XMAX.  However, that mechanism will release all
 * waiters concurrently, so there would be a race condition as to which
 * waiter gets the tuple, potentially leading to indefinite starvation of
 * some waiters.  The possibility of share-locking makes the problem much
 * worse --- a steady stream of share-lockers can easily block an exclusive
 * locker forever.      To provide more reliable semantics about who gets a
 * tuple-level lock first, we use the standard lock manager.  The protocol
 * for waiting for a tuple-level lock is really
 *          LockTuple()
 *          XactLockTableWait()
 *          mark tuple as locked by me
 *          UnlockTuple()
 * When there are multiple waiters, arbitration of who is to get the lock next
 * is provided by LockTuple().      However, at most one tuple-level lock will
 * be held or awaited per backend at any time, so we don't risk overflow
 * of the lock table.  Note that incoming share-lockers are required to
 * do LockTuple as well, if there is any conflict, to ensure that they don't
 * starve out waiting exclusive-lockers.  However, if there is not any active
 * conflict for a tuple, we don't incur any extra overhead.
 */
HTSU_Result
heap_lock_tuple(Relation relation, HeapTuple tuple, Buffer *buffer,
                        ItemPointer ctid, TransactionId *update_xmax,
                        CommandId cid, LockTupleMode mode, bool nowait)
{
      HTSU_Result result;
      ItemPointer tid = &(tuple->t_self);
      ItemId            lp;
      Page        page;
      TransactionId xid;
      TransactionId xmax;
      uint16            old_infomask;
      uint16            new_infomask;
      LOCKMODE    tuple_lock_type;
      bool        have_tuple_lock = false;

      tuple_lock_type = (mode == LockTupleShared) ? ShareLock : ExclusiveLock;

      *buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(tid));
      LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

      page = BufferGetPage(*buffer);
      lp = PageGetItemId(page, ItemPointerGetOffsetNumber(tid));
      Assert(ItemIdIsNormal(lp));

      tuple->t_data = (HeapTupleHeader) PageGetItem(page, lp);
      tuple->t_len = ItemIdGetLength(lp);
      tuple->t_tableOid = RelationGetRelid(relation);

l3:
      result = HeapTupleSatisfiesUpdate(tuple->t_data, cid, *buffer);

      if (result == HeapTupleInvisible)
      {
            UnlockReleaseBuffer(*buffer);
            elog(ERROR, "attempted to lock invisible tuple");
      }
      else if (result == HeapTupleBeingUpdated)
      {
            TransactionId xwait;
            uint16            infomask;

            /* must copy state data before unlocking buffer */
            xwait = HeapTupleHeaderGetXmax(tuple->t_data);
            infomask = tuple->t_data->t_infomask;

            LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);

            /*
             * If we wish to acquire share lock, and the tuple is already
             * share-locked by a multixact that includes any subtransaction of the
             * current top transaction, then we effectively hold the desired lock
             * already.  We *must* succeed without trying to take the tuple lock,
             * else we will deadlock against anyone waiting to acquire exclusive
             * lock.  We don't need to make any state changes in this case.
             */
            if (mode == LockTupleShared &&
                  (infomask & HEAP_XMAX_IS_MULTI) &&
                  MultiXactIdIsCurrent((MultiXactId) xwait))
            {
                  Assert(infomask & HEAP_XMAX_SHARED_LOCK);
                  /* Probably can't hold tuple lock here, but may as well check */
                  if (have_tuple_lock)
                        UnlockTuple(relation, tid, tuple_lock_type);
                  return HeapTupleMayBeUpdated;
            }

            /*
             * Acquire tuple lock to establish our priority for the tuple.
             * LockTuple will release us when we are next-in-line for the tuple.
             * We must do this even if we are share-locking.
             *
             * If we are forced to "start over" below, we keep the tuple lock;
             * this arranges that we stay at the head of the line while rechecking
             * tuple state.
             */
            if (!have_tuple_lock)
            {
                  if (nowait)
                  {
                        if (!ConditionalLockTuple(relation, tid, tuple_lock_type))
                              ereport(ERROR,
                                          (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                              errmsg("could not obtain lock on row in relation \"%s\"",
                                       RelationGetRelationName(relation))));
                  }
                  else
                        LockTuple(relation, tid, tuple_lock_type);
                  have_tuple_lock = true;
            }

            if (mode == LockTupleShared && (infomask & HEAP_XMAX_SHARED_LOCK))
            {
                  /*
                   * Acquiring sharelock when there's at least one sharelocker
                   * already.  We need not wait for him/them to complete.
                   */
                  LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

                  /*
                   * Make sure it's still a shared lock, else start over.  (It's OK
                   * if the ownership of the shared lock has changed, though.)
                   */
                  if (!(tuple->t_data->t_infomask & HEAP_XMAX_SHARED_LOCK))
                        goto l3;
            }
            else if (infomask & HEAP_XMAX_IS_MULTI)
            {
                  /* wait for multixact to end */
                  if (nowait)
                  {
                        if (!ConditionalMultiXactIdWait((MultiXactId) xwait))
                              ereport(ERROR,
                                          (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                              errmsg("could not obtain lock on row in relation \"%s\"",
                                       RelationGetRelationName(relation))));
                  }
                  else
                        MultiXactIdWait((MultiXactId) xwait);

                  LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

                  /*
                   * If xwait had just locked the tuple then some other xact could
                   * update this tuple before we get to this point. Check for xmax
                   * change, and start over if so.
                   */
                  if (!(tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
                        !TransactionIdEquals(HeapTupleHeaderGetXmax(tuple->t_data),
                                                       xwait))
                        goto l3;

                  /*
                   * You might think the multixact is necessarily done here, but not
                   * so: it could have surviving members, namely our own xact or
                   * other subxacts of this backend.  It is legal for us to lock the
                   * tuple in either case, however.  We don't bother changing the
                   * on-disk hint bits since we are about to overwrite the xmax
                   * altogether.
                   */
            }
            else
            {
                  /* wait for regular transaction to end */
                  if (nowait)
                  {
                        if (!ConditionalXactLockTableWait(xwait))
                              ereport(ERROR,
                                          (errcode(ERRCODE_LOCK_NOT_AVAILABLE),
                              errmsg("could not obtain lock on row in relation \"%s\"",
                                       RelationGetRelationName(relation))));
                  }
                  else
                        XactLockTableWait(xwait);

                  LockBuffer(*buffer, BUFFER_LOCK_EXCLUSIVE);

                  /*
                   * xwait is done, but if xwait had just locked the tuple then some
                   * other xact could update this tuple before we get to this point.
                   * Check for xmax change, and start over if so.
                   */
                  if ((tuple->t_data->t_infomask & HEAP_XMAX_IS_MULTI) ||
                        !TransactionIdEquals(HeapTupleHeaderGetXmax(tuple->t_data),
                                                       xwait))
                        goto l3;

                  /* Otherwise check if it committed or aborted */
                  UpdateXmaxHintBits(tuple->t_data, *buffer, xwait);
            }

            /*
             * We may lock if previous xmax aborted, or if it committed but only
             * locked the tuple without updating it.  The case where we didn't
             * wait because we are joining an existing shared lock is correctly
             * handled, too.
             */
            if (tuple->t_data->t_infomask & (HEAP_XMAX_INVALID |
                                                             HEAP_IS_LOCKED))
                  result = HeapTupleMayBeUpdated;
            else
                  result = HeapTupleUpdated;
      }

      if (result != HeapTupleMayBeUpdated)
      {
            Assert(result == HeapTupleSelfUpdated || result == HeapTupleUpdated);
            Assert(!(tuple->t_data->t_infomask & HEAP_XMAX_INVALID));
            *ctid = tuple->t_data->t_ctid;
            *update_xmax = HeapTupleHeaderGetXmax(tuple->t_data);
            LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
            if (have_tuple_lock)
                  UnlockTuple(relation, tid, tuple_lock_type);
            return result;
      }

      /*
       * We might already hold the desired lock (or stronger), possibly under a
       * different subtransaction of the current top transaction.  If so, there
       * is no need to change state or issue a WAL record.  We already handled
       * the case where this is true for xmax being a MultiXactId, so now check
       * for cases where it is a plain TransactionId.
       *
       * Note in particular that this covers the case where we already hold
       * exclusive lock on the tuple and the caller only wants shared lock. It
       * would certainly not do to give up the exclusive lock.
       */
      xmax = HeapTupleHeaderGetXmax(tuple->t_data);
      old_infomask = tuple->t_data->t_infomask;

      if (!(old_infomask & (HEAP_XMAX_INVALID |
                                      HEAP_XMAX_COMMITTED |
                                      HEAP_XMAX_IS_MULTI)) &&
            (mode == LockTupleShared ?
             (old_infomask & HEAP_IS_LOCKED) :
             (old_infomask & HEAP_XMAX_EXCL_LOCK)) &&
            TransactionIdIsCurrentTransactionId(xmax))
      {
            LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);
            /* Probably can't hold tuple lock here, but may as well check */
            if (have_tuple_lock)
                  UnlockTuple(relation, tid, tuple_lock_type);
            return HeapTupleMayBeUpdated;
      }

      /*
       * Compute the new xmax and infomask to store into the tuple.  Note we do
       * not modify the tuple just yet, because that would leave it in the wrong
       * state if multixact.c elogs.
       */
      xid = GetCurrentTransactionId();

      new_infomask = old_infomask & ~(HEAP_XMAX_COMMITTED |
                                                      HEAP_XMAX_INVALID |
                                                      HEAP_XMAX_IS_MULTI |
                                                      HEAP_IS_LOCKED |
                                                      HEAP_MOVED);

      if (mode == LockTupleShared)
      {
            /*
             * If this is the first acquisition of a shared lock in the current
             * transaction, set my per-backend OldestMemberMXactId setting. We can
             * be certain that the transaction will never become a member of any
             * older MultiXactIds than that.  (We have to do this even if we end
             * up just using our own TransactionId below, since some other backend
             * could incorporate our XID into a MultiXact immediately afterwards.)
             */
            MultiXactIdSetOldestMember();

            new_infomask |= HEAP_XMAX_SHARED_LOCK;

            /*
             * Check to see if we need a MultiXactId because there are multiple
             * lockers.
             *
             * HeapTupleSatisfiesUpdate will have set the HEAP_XMAX_INVALID bit if
             * the xmax was a MultiXactId but it was not running anymore. There is
             * a race condition, which is that the MultiXactId may have finished
             * since then, but that uncommon case is handled within
             * MultiXactIdExpand.
             *
             * There is a similar race condition possible when the old xmax was a
             * regular TransactionId.  We test TransactionIdIsInProgress again
             * just to narrow the window, but it's still possible to end up
             * creating an unnecessary MultiXactId.  Fortunately this is harmless.
             */
            if (!(old_infomask & (HEAP_XMAX_INVALID | HEAP_XMAX_COMMITTED)))
            {
                  if (old_infomask & HEAP_XMAX_IS_MULTI)
                  {
                        /*
                         * If the XMAX is already a MultiXactId, then we need to
                         * expand it to include our own TransactionId.
                         */
                        xid = MultiXactIdExpand((MultiXactId) xmax, xid);
                        new_infomask |= HEAP_XMAX_IS_MULTI;
                  }
                  else if (TransactionIdIsInProgress(xmax))
                  {
                        /*
                         * If the XMAX is a valid TransactionId, then we need to
                         * create a new MultiXactId that includes both the old locker
                         * and our own TransactionId.
                         */
                        xid = MultiXactIdCreate(xmax, xid);
                        new_infomask |= HEAP_XMAX_IS_MULTI;
                  }
                  else
                  {
                        /*
                         * Can get here iff HeapTupleSatisfiesUpdate saw the old xmax
                         * as running, but it finished before
                         * TransactionIdIsInProgress() got to run.      Treat it like
                         * there's no locker in the tuple.
                         */
                  }
            }
            else
            {
                  /*
                   * There was no previous locker, so just insert our own
                   * TransactionId.
                   */
            }
      }
      else
      {
            /* We want an exclusive lock on the tuple */
            new_infomask |= HEAP_XMAX_EXCL_LOCK;
      }

      START_CRIT_SECTION();

      /*
       * Store transaction information of xact locking the tuple.
       *
       * Note: Cmax is meaningless in this context, so don't set it; this avoids
       * possibly generating a useless combo CID.
       */
      tuple->t_data->t_infomask = new_infomask;
      HeapTupleHeaderClearHotUpdated(tuple->t_data);
      HeapTupleHeaderSetXmax(tuple->t_data, xid);
      /* Make sure there is no forward chain link in t_ctid */
      tuple->t_data->t_ctid = *tid;

      MarkBufferDirty(*buffer);

      /*
       * XLOG stuff.    You might think that we don't need an XLOG record because
       * there is no state change worth restoring after a crash.  You would be
       * wrong however: we have just written either a TransactionId or a
       * MultiXactId that may never have been seen on disk before, and we need
       * to make sure that there are XLOG entries covering those ID numbers.
       * Else the same IDs might be re-used after a crash, which would be
       * disastrous if this page made it to disk before the crash.  Essentially
       * we have to enforce the WAL log-before-data rule even in this case.
       * (Also, in a PITR log-shipping or 2PC environment, we have to have XLOG
       * entries for everything anyway.)
       */
      if (!relation->rd_istemp)
      {
            xl_heap_lock xlrec;
            XLogRecPtr  recptr;
            XLogRecData rdata[2];

            xlrec.target.node = relation->rd_node;
            xlrec.target.tid = tuple->t_self;
            xlrec.locking_xid = xid;
            xlrec.xid_is_mxact = ((new_infomask & HEAP_XMAX_IS_MULTI) != 0);
            xlrec.shared_lock = (mode == LockTupleShared);
            rdata[0].data = (char *) &xlrec;
            rdata[0].len = SizeOfHeapLock;
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &(rdata[1]);

            rdata[1].data = NULL;
            rdata[1].len = 0;
            rdata[1].buffer = *buffer;
            rdata[1].buffer_std = true;
            rdata[1].next = NULL;

            recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_LOCK, rdata);

            PageSetLSN(page, recptr);
            PageSetTLI(page, ThisTimeLineID);
      }

      END_CRIT_SECTION();

      LockBuffer(*buffer, BUFFER_LOCK_UNLOCK);

      /*
       * Don't update the visibility map here. Locking a tuple doesn't change
       * visibility info.
       */

      /*
       * Now that we have successfully marked the tuple as locked, we can
       * release the lmgr tuple lock, if we had it.
       */
      if (have_tuple_lock)
            UnlockTuple(relation, tid, tuple_lock_type);

      return HeapTupleMayBeUpdated;
}


/*
 * heap_inplace_update - update a tuple "in place" (ie, overwrite it)
 *
 * Overwriting violates both MVCC and transactional safety, so the uses
 * of this function in Postgres are extremely limited.      Nonetheless we
 * find some places to use it.
 *
 * The tuple cannot change size, and therefore it's reasonable to assume
 * that its null bitmap (if any) doesn't change either.  So we just
 * overwrite the data portion of the tuple without touching the null
 * bitmap or any of the header fields.
 *
 * tuple is an in-memory tuple structure containing the data to be written
 * over the target tuple.  Also, tuple->t_self identifies the target tuple.
 */
void
heap_inplace_update(Relation relation, HeapTuple tuple)
{
      Buffer            buffer;
      Page        page;
      OffsetNumber offnum;
      ItemId            lp = NULL;
      HeapTupleHeader htup;
      uint32            oldlen;
      uint32            newlen;

      buffer = ReadBuffer(relation, ItemPointerGetBlockNumber(&(tuple->t_self)));
      LockBuffer(buffer, BUFFER_LOCK_EXCLUSIVE);
      page = (Page) BufferGetPage(buffer);

      offnum = ItemPointerGetOffsetNumber(&(tuple->t_self));
      if (PageGetMaxOffsetNumber(page) >= offnum)
            lp = PageGetItemId(page, offnum);

      if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
            elog(ERROR, "heap_inplace_update: invalid lp");

      htup = (HeapTupleHeader) PageGetItem(page, lp);

      oldlen = ItemIdGetLength(lp) - htup->t_hoff;
      newlen = tuple->t_len - tuple->t_data->t_hoff;
      if (oldlen != newlen || htup->t_hoff != tuple->t_data->t_hoff)
            elog(ERROR, "heap_inplace_update: wrong tuple length");

      /* NO EREPORT(ERROR) from here till changes are logged */
      START_CRIT_SECTION();

      memcpy((char *) htup + htup->t_hoff,
               (char *) tuple->t_data + tuple->t_data->t_hoff,
               newlen);

      MarkBufferDirty(buffer);

      /* XLOG stuff */
      if (!relation->rd_istemp)
      {
            xl_heap_inplace xlrec;
            XLogRecPtr  recptr;
            XLogRecData rdata[2];

            xlrec.target.node = relation->rd_node;
            xlrec.target.tid = tuple->t_self;

            rdata[0].data = (char *) &xlrec;
            rdata[0].len = SizeOfHeapInplace;
            rdata[0].buffer = InvalidBuffer;
            rdata[0].next = &(rdata[1]);

            rdata[1].data = (char *) htup + htup->t_hoff;
            rdata[1].len = newlen;
            rdata[1].buffer = buffer;
            rdata[1].buffer_std = true;
            rdata[1].next = NULL;

            recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_INPLACE, rdata);

            PageSetLSN(page, recptr);
            PageSetTLI(page, ThisTimeLineID);
      }

      END_CRIT_SECTION();

      UnlockReleaseBuffer(buffer);

      /* Send out shared cache inval if necessary */
      if (!IsBootstrapProcessingMode())
            CacheInvalidateHeapTuple(relation, tuple);
}


/*
 * heap_freeze_tuple
 *
 * Check to see whether any of the XID fields of a tuple (xmin, xmax, xvac)
 * are older than the specified cutoff XID.  If so, replace them with
 * FrozenTransactionId or InvalidTransactionId as appropriate, and return
 * TRUE.  Return FALSE if nothing was changed.
 *
 * It is assumed that the caller has checked the tuple with
 * HeapTupleSatisfiesVacuum() and determined that it is not HEAPTUPLE_DEAD
 * (else we should be removing the tuple, not freezing it).
 *
 * NB: cutoff_xid *must* be <= the current global xmin, to ensure that any
 * XID older than it could neither be running nor seen as running by any
 * open transaction.  This ensures that the replacement will not change
 * anyone's idea of the tuple state.  Also, since we assume the tuple is
 * not HEAPTUPLE_DEAD, the fact that an XID is not still running allows us
 * to assume that it is either committed good or aborted, as appropriate;
 * so we need no external state checks to decide what to do.  (This is good
 * because this function is applied during WAL recovery, when we don't have
 * access to any such state, and can't depend on the hint bits to be set.)
 *
 * In lazy VACUUM, we call this while initially holding only a shared lock
 * on the tuple's buffer.  If any change is needed, we trade that in for an
 * exclusive lock before making the change.  Caller should pass the buffer ID
 * if shared lock is held, InvalidBuffer if exclusive lock is already held.
 *
 * Note: it might seem we could make the changes without exclusive lock, since
 * TransactionId read/write is assumed atomic anyway.  However there is a race
 * condition: someone who just fetched an old XID that we overwrite here could
 * conceivably not finish checking the XID against pg_clog before we finish
 * the VACUUM and perhaps truncate off the part of pg_clog he needs.  Getting
 * exclusive lock ensures no other backend is in process of checking the
 * tuple status.  Also, getting exclusive lock makes it safe to adjust the
 * infomask bits.
 */
bool
heap_freeze_tuple(HeapTupleHeader tuple, TransactionId cutoff_xid,
                          Buffer buf)
{
      bool        changed = false;
      TransactionId xid;

      xid = HeapTupleHeaderGetXmin(tuple);
      if (TransactionIdIsNormal(xid) &&
            TransactionIdPrecedes(xid, cutoff_xid))
      {
            if (buf != InvalidBuffer)
            {
                  /* trade in share lock for exclusive lock */
                  LockBuffer(buf, BUFFER_LOCK_UNLOCK);
                  LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
                  buf = InvalidBuffer;
            }
            HeapTupleHeaderSetXmin(tuple, FrozenTransactionId);

            /*
             * Might as well fix the hint bits too; usually XMIN_COMMITTED will
             * already be set here, but there's a small chance not.
             */
            Assert(!(tuple->t_infomask & HEAP_XMIN_INVALID));
            tuple->t_infomask |= HEAP_XMIN_COMMITTED;
            changed = true;
      }

      /*
       * When we release shared lock, it's possible for someone else to change
       * xmax before we get the lock back, so repeat the check after acquiring
       * exclusive lock.      (We don't need this pushup for xmin, because only
       * VACUUM could be interested in changing an existing tuple's xmin, and
       * there's only one VACUUM allowed on a table at a time.)
       */
recheck_xmax:
      if (!(tuple->t_infomask & HEAP_XMAX_IS_MULTI))
      {
            xid = HeapTupleHeaderGetXmax(tuple);
            if (TransactionIdIsNormal(xid) &&
                  TransactionIdPrecedes(xid, cutoff_xid))
            {
                  if (buf != InvalidBuffer)
                  {
                        /* trade in share lock for exclusive lock */
                        LockBuffer(buf, BUFFER_LOCK_UNLOCK);
                        LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
                        buf = InvalidBuffer;
                        goto recheck_xmax;            /* see comment above */
                  }
                  HeapTupleHeaderSetXmax(tuple, InvalidTransactionId);

                  /*
                   * The tuple might be marked either XMAX_INVALID or XMAX_COMMITTED
                   * + LOCKED.  Normalize to INVALID just to be sure no one gets
                   * confused.
                   */
                  tuple->t_infomask &= ~HEAP_XMAX_COMMITTED;
                  tuple->t_infomask |= HEAP_XMAX_INVALID;
                  HeapTupleHeaderClearHotUpdated(tuple);
                  changed = true;
            }
      }
      else
      {
            /*----------
             * XXX perhaps someday we should zero out very old MultiXactIds here?
             *
             * The only way a stale MultiXactId could pose a problem is if a
             * tuple, having once been multiply-share-locked, is not touched by
             * any vacuum or attempted lock or deletion for just over 4G MultiXact
             * creations, and then in the probably-narrow window where its xmax
             * is again a live MultiXactId, someone tries to lock or delete it.
             * Even then, another share-lock attempt would work fine.  An
             * exclusive-lock or delete attempt would face unexpected delay, or
             * in the very worst case get a deadlock error.  This seems an
             * extremely low-probability scenario with minimal downside even if
             * it does happen, so for now we don't do the extra bookkeeping that
             * would be needed to clean out MultiXactIds.
             *----------
             */
      }

      /*
       * Although xvac per se could only be set by VACUUM, it shares physical
       * storage space with cmax, and so could be wiped out by someone setting
       * xmax.  Hence recheck after changing lock, same as for xmax itself.
       */
recheck_xvac:
      if (tuple->t_infomask & HEAP_MOVED)
      {
            xid = HeapTupleHeaderGetXvac(tuple);
            if (TransactionIdIsNormal(xid) &&
                  TransactionIdPrecedes(xid, cutoff_xid))
            {
                  if (buf != InvalidBuffer)
                  {
                        /* trade in share lock for exclusive lock */
                        LockBuffer(buf, BUFFER_LOCK_UNLOCK);
                        LockBuffer(buf, BUFFER_LOCK_EXCLUSIVE);
                        buf = InvalidBuffer;
                        goto recheck_xvac;            /* see comment above */
                  }

                  /*
                   * If a MOVED_OFF tuple is not dead, the xvac transaction must
                   * have failed; whereas a non-dead MOVED_IN tuple must mean the
                   * xvac transaction succeeded.
                   */
                  if (tuple->t_infomask & HEAP_MOVED_OFF)
                        HeapTupleHeaderSetXvac(tuple, InvalidTransactionId);
                  else
                        HeapTupleHeaderSetXvac(tuple, FrozenTransactionId);

                  /*
                   * Might as well fix the hint bits too; usually XMIN_COMMITTED
                   * will already be set here, but there's a small chance not.
                   */
                  Assert(!(tuple->t_infomask & HEAP_XMIN_INVALID));
                  tuple->t_infomask |= HEAP_XMIN_COMMITTED;
                  changed = true;
            }
      }

      return changed;
}


/* ----------------
 *          heap_markpos      - mark scan position
 * ----------------
 */
void
heap_markpos(HeapScanDesc scan)
{
      /* Note: no locking manipulations needed */

      if (scan->rs_ctup.t_data != NULL)
      {
            scan->rs_mctid = scan->rs_ctup.t_self;
            if (scan->rs_pageatatime)
                  scan->rs_mindex = scan->rs_cindex;
      }
      else
            ItemPointerSetInvalid(&scan->rs_mctid);
}

/* ----------------
 *          heap_restrpos     - restore position to marked location
 * ----------------
 */
void
heap_restrpos(HeapScanDesc scan)
{
      /* XXX no amrestrpos checking that ammarkpos called */

      if (!ItemPointerIsValid(&scan->rs_mctid))
      {
            scan->rs_ctup.t_data = NULL;

            /*
             * unpin scan buffers
             */
            if (BufferIsValid(scan->rs_cbuf))
                  ReleaseBuffer(scan->rs_cbuf);
            scan->rs_cbuf = InvalidBuffer;
            scan->rs_cblock = InvalidBlockNumber;
            scan->rs_inited = false;
      }
      else
      {
            /*
             * If we reached end of scan, rs_inited will now be false.  We must
             * reset it to true to keep heapgettup from doing the wrong thing.
             */
            scan->rs_inited = true;
            scan->rs_ctup.t_self = scan->rs_mctid;
            if (scan->rs_pageatatime)
            {
                  scan->rs_cindex = scan->rs_mindex;
                  heapgettup_pagemode(scan,
                                                NoMovementScanDirection,
                                                0,          /* needn't recheck scan keys */
                                                NULL);
            }
            else
                  heapgettup(scan,
                                 NoMovementScanDirection,
                                 0,       /* needn't recheck scan keys */
                                 NULL);
      }
}

/*
 * Perform XLogInsert for a heap-clean operation.  Caller must already
 * have modified the buffer and marked it dirty.
 *
 * Note: prior to Postgres 8.3, the entries in the nowunused[] array were
 * zero-based tuple indexes.  Now they are one-based like other uses
 * of OffsetNumber.
 */
XLogRecPtr
log_heap_clean(Relation reln, Buffer buffer,
                     OffsetNumber *redirected, int nredirected,
                     OffsetNumber *nowdead, int ndead,
                     OffsetNumber *nowunused, int nunused,
                     bool redirect_move)
{
      xl_heap_clean xlrec;
      uint8       info;
      XLogRecPtr  recptr;
      XLogRecData rdata[4];

      /* Caller should not call me on a temp relation */
      Assert(!reln->rd_istemp);

      xlrec.node = reln->rd_node;
      xlrec.block = BufferGetBlockNumber(buffer);
      xlrec.nredirected = nredirected;
      xlrec.ndead = ndead;

      rdata[0].data = (char *) &xlrec;
      rdata[0].len = SizeOfHeapClean;
      rdata[0].buffer = InvalidBuffer;
      rdata[0].next = &(rdata[1]);

      /*
       * The OffsetNumber arrays are not actually in the buffer, but we pretend
       * that they are.  When XLogInsert stores the whole buffer, the offset
       * arrays need not be stored too.  Note that even if all three arrays are
       * empty, we want to expose the buffer as a candidate for whole-page
       * storage, since this record type implies a defragmentation operation
       * even if no item pointers changed state.
       */
      if (nredirected > 0)
      {
            rdata[1].data = (char *) redirected;
            rdata[1].len = nredirected * sizeof(OffsetNumber) * 2;
      }
      else
      {
            rdata[1].data = NULL;
            rdata[1].len = 0;
      }
      rdata[1].buffer = buffer;
      rdata[1].buffer_std = true;
      rdata[1].next = &(rdata[2]);

      if (ndead > 0)
      {
            rdata[2].data = (char *) nowdead;
            rdata[2].len = ndead * sizeof(OffsetNumber);
      }
      else
      {
            rdata[2].data = NULL;
            rdata[2].len = 0;
      }
      rdata[2].buffer = buffer;
      rdata[2].buffer_std = true;
      rdata[2].next = &(rdata[3]);

      if (nunused > 0)
      {
            rdata[3].data = (char *) nowunused;
            rdata[3].len = nunused * sizeof(OffsetNumber);
      }
      else
      {
            rdata[3].data = NULL;
            rdata[3].len = 0;
      }
      rdata[3].buffer = buffer;
      rdata[3].buffer_std = true;
      rdata[3].next = NULL;

      info = redirect_move ? XLOG_HEAP2_CLEAN_MOVE : XLOG_HEAP2_CLEAN;
      recptr = XLogInsert(RM_HEAP2_ID, info, rdata);

      return recptr;
}

/*
 * Perform XLogInsert for a heap-freeze operation.    Caller must already
 * have modified the buffer and marked it dirty.
 */
XLogRecPtr
log_heap_freeze(Relation reln, Buffer buffer,
                        TransactionId cutoff_xid,
                        OffsetNumber *offsets, int offcnt)
{
      xl_heap_freeze xlrec;
      XLogRecPtr  recptr;
      XLogRecData rdata[2];

      /* Caller should not call me on a temp relation */
      Assert(!reln->rd_istemp);
      /* nor when there are no tuples to freeze */
      Assert(offcnt > 0);

      xlrec.node = reln->rd_node;
      xlrec.block = BufferGetBlockNumber(buffer);
      xlrec.cutoff_xid = cutoff_xid;

      rdata[0].data = (char *) &xlrec;
      rdata[0].len = SizeOfHeapFreeze;
      rdata[0].buffer = InvalidBuffer;
      rdata[0].next = &(rdata[1]);

      /*
       * The tuple-offsets array is not actually in the buffer, but pretend that
       * it is.  When XLogInsert stores the whole buffer, the offsets array need
       * not be stored too.
       */
      rdata[1].data = (char *) offsets;
      rdata[1].len = offcnt * sizeof(OffsetNumber);
      rdata[1].buffer = buffer;
      rdata[1].buffer_std = true;
      rdata[1].next = NULL;

      recptr = XLogInsert(RM_HEAP2_ID, XLOG_HEAP2_FREEZE, rdata);

      return recptr;
}

/*
 * Perform XLogInsert for a heap-update operation.    Caller must already
 * have modified the buffer(s) and marked them dirty.
 */
static XLogRecPtr
log_heap_update(Relation reln, Buffer oldbuf, ItemPointerData from,
                        Buffer newbuf, HeapTuple newtup, bool move)
{
      /*
       * Note: xlhdr is declared to have adequate size and correct alignment for
       * an xl_heap_header.  However the two tids, if present at all, will be
       * packed in with no wasted space after the xl_heap_header; they aren't
       * necessarily aligned as implied by this struct declaration.
       */
      struct
      {
            xl_heap_header hdr;
            TransactionId tid1;
            TransactionId tid2;
      }                 xlhdr;
      int               hsize = SizeOfHeapHeader;
      xl_heap_update xlrec;
      uint8       info;
      XLogRecPtr  recptr;
      XLogRecData rdata[4];
      Page        page = BufferGetPage(newbuf);

      /* Caller should not call me on a temp relation */
      Assert(!reln->rd_istemp);

      if (move)
      {
            Assert(!HeapTupleIsHeapOnly(newtup));
            info = XLOG_HEAP_MOVE;
      }
      else if (HeapTupleIsHeapOnly(newtup))
            info = XLOG_HEAP_HOT_UPDATE;
      else
            info = XLOG_HEAP_UPDATE;

      xlrec.target.node = reln->rd_node;
      xlrec.target.tid = from;
      xlrec.all_visible_cleared = PageIsAllVisible(BufferGetPage(oldbuf));
      xlrec.newtid = newtup->t_self;
      xlrec.new_all_visible_cleared = PageIsAllVisible(BufferGetPage(newbuf));

      rdata[0].data = (char *) &xlrec;
      rdata[0].len = SizeOfHeapUpdate;
      rdata[0].buffer = InvalidBuffer;
      rdata[0].next = &(rdata[1]);

      rdata[1].data = NULL;
      rdata[1].len = 0;
      rdata[1].buffer = oldbuf;
      rdata[1].buffer_std = true;
      rdata[1].next = &(rdata[2]);

      xlhdr.hdr.t_infomask2 = newtup->t_data->t_infomask2;
      xlhdr.hdr.t_infomask = newtup->t_data->t_infomask;
      xlhdr.hdr.t_hoff = newtup->t_data->t_hoff;
      if (move)                           /* remember xmax & xmin */
      {
            TransactionId xid[2];   /* xmax, xmin */

            if (newtup->t_data->t_infomask & (HEAP_XMAX_INVALID | HEAP_IS_LOCKED))
                  xid[0] = InvalidTransactionId;
            else
                  xid[0] = HeapTupleHeaderGetXmax(newtup->t_data);
            xid[1] = HeapTupleHeaderGetXmin(newtup->t_data);
            memcpy((char *) &xlhdr + hsize,
                     (char *) xid,
                     2 * sizeof(TransactionId));
            hsize += 2 * sizeof(TransactionId);
      }

      /*
       * As with insert records, we need not store the rdata[2] segment if we
       * decide to store the whole buffer instead.
       */
      rdata[2].data = (char *) &xlhdr;
      rdata[2].len = hsize;
      rdata[2].buffer = newbuf;
      rdata[2].buffer_std = true;
      rdata[2].next = &(rdata[3]);

      /* PG73FORMAT: write bitmap [+ padding] [+ oid] + data */
      rdata[3].data = (char *) newtup->t_data + offsetof(HeapTupleHeaderData, t_bits);
      rdata[3].len = newtup->t_len - offsetof(HeapTupleHeaderData, t_bits);
      rdata[3].buffer = newbuf;
      rdata[3].buffer_std = true;
      rdata[3].next = NULL;

      /* If new tuple is the single and first tuple on page... */
      if (ItemPointerGetOffsetNumber(&(newtup->t_self)) == FirstOffsetNumber &&
            PageGetMaxOffsetNumber(page) == FirstOffsetNumber)
      {
            info |= XLOG_HEAP_INIT_PAGE;
            rdata[2].buffer = rdata[3].buffer = InvalidBuffer;
      }

      recptr = XLogInsert(RM_HEAP_ID, info, rdata);

      return recptr;
}

/*
 * Perform XLogInsert for a heap-move operation.  Caller must already
 * have modified the buffers and marked them dirty.
 */
XLogRecPtr
log_heap_move(Relation reln, Buffer oldbuf, ItemPointerData from,
                    Buffer newbuf, HeapTuple newtup)
{
      return log_heap_update(reln, oldbuf, from, newbuf, newtup, true);
}

/*
 * Perform XLogInsert of a HEAP_NEWPAGE record to WAL. Caller is responsible
 * for writing the page to disk after calling this routine.
 *
 * Note: all current callers build pages in private memory and write them
 * directly to smgr, rather than using bufmgr.  Therefore there is no need
 * to pass a buffer ID to XLogInsert, nor to perform MarkBufferDirty within
 * the critical section.
 *
 * Note: the NEWPAGE log record is used for both heaps and indexes, so do
 * not do anything that assumes we are touching a heap.
 */
XLogRecPtr
log_newpage(RelFileNode *rnode, ForkNumber forkNum, BlockNumber blkno,
                  Page page)
{
      xl_heap_newpage xlrec;
      XLogRecPtr  recptr;
      XLogRecData rdata[2];

      /* NO ELOG(ERROR) from here till newpage op is logged */
      START_CRIT_SECTION();

      xlrec.node = *rnode;
      xlrec.forknum = forkNum;
      xlrec.blkno = blkno;

      rdata[0].data = (char *) &xlrec;
      rdata[0].len = SizeOfHeapNewpage;
      rdata[0].buffer = InvalidBuffer;
      rdata[0].next = &(rdata[1]);

      rdata[1].data = (char *) page;
      rdata[1].len = BLCKSZ;
      rdata[1].buffer = InvalidBuffer;
      rdata[1].next = NULL;

      recptr = XLogInsert(RM_HEAP_ID, XLOG_HEAP_NEWPAGE, rdata);

      PageSetLSN(page, recptr);
      PageSetTLI(page, ThisTimeLineID);

      END_CRIT_SECTION();

      return recptr;
}

/*
 * Handles CLEAN and CLEAN_MOVE record types
 */
static void
heap_xlog_clean(XLogRecPtr lsn, XLogRecord *record, bool clean_move)
{
      xl_heap_clean *xlrec = (xl_heap_clean *) XLogRecGetData(record);
      Buffer            buffer;
      Page        page;
      OffsetNumber *end;
      OffsetNumber *redirected;
      OffsetNumber *nowdead;
      OffsetNumber *nowunused;
      int               nredirected;
      int               ndead;
      int               nunused;
      Size        freespace;

      if (record->xl_info & XLR_BKP_BLOCK_1)
            return;

      buffer = XLogReadBuffer(xlrec->node, xlrec->block, false);
      if (!BufferIsValid(buffer))
            return;
      page = (Page) BufferGetPage(buffer);

      if (XLByteLE(lsn, PageGetLSN(page)))
      {
            UnlockReleaseBuffer(buffer);
            return;
      }

      nredirected = xlrec->nredirected;
      ndead = xlrec->ndead;
      end = (OffsetNumber *) ((char *) xlrec + record->xl_len);
      redirected = (OffsetNumber *) ((char *) xlrec + SizeOfHeapClean);
      nowdead = redirected + (nredirected * 2);
      nowunused = nowdead + ndead;
      nunused = (end - nowunused);
      Assert(nunused >= 0);

      /* Update all item pointers per the record, and repair fragmentation */
      heap_page_prune_execute(buffer,
                                          redirected, nredirected,
                                          nowdead, ndead,
                                          nowunused, nunused,
                                          clean_move);

      freespace = PageGetHeapFreeSpace(page);         /* needed to update FSM below */

      /*
       * Note: we don't worry about updating the page's prunability hints. At
       * worst this will cause an extra prune cycle to occur soon.
       */

      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);

      /*
       * Update the FSM as well.
       *
       * XXX: We don't get here if the page was restored from full page image.
       * We don't bother to update the FSM in that case, it doesn't need to be
       * totally accurate anyway.
       */
      XLogRecordPageWithFreeSpace(xlrec->node, xlrec->block, freespace);
}

static void
heap_xlog_freeze(XLogRecPtr lsn, XLogRecord *record)
{
      xl_heap_freeze *xlrec = (xl_heap_freeze *) XLogRecGetData(record);
      TransactionId cutoff_xid = xlrec->cutoff_xid;
      Buffer            buffer;
      Page        page;

      if (record->xl_info & XLR_BKP_BLOCK_1)
            return;

      buffer = XLogReadBuffer(xlrec->node, xlrec->block, false);
      if (!BufferIsValid(buffer))
            return;
      page = (Page) BufferGetPage(buffer);

      if (XLByteLE(lsn, PageGetLSN(page)))
      {
            UnlockReleaseBuffer(buffer);
            return;
      }

      if (record->xl_len > SizeOfHeapFreeze)
      {
            OffsetNumber *offsets;
            OffsetNumber *offsets_end;

            offsets = (OffsetNumber *) ((char *) xlrec + SizeOfHeapFreeze);
            offsets_end = (OffsetNumber *) ((char *) xlrec + record->xl_len);

            while (offsets < offsets_end)
            {
                  /* offsets[] entries are one-based */
                  ItemId            lp = PageGetItemId(page, *offsets);
                  HeapTupleHeader tuple = (HeapTupleHeader) PageGetItem(page, lp);

                  (void) heap_freeze_tuple(tuple, cutoff_xid, InvalidBuffer);
                  offsets++;
            }
      }

      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);
}

static void
heap_xlog_newpage(XLogRecPtr lsn, XLogRecord *record)
{
      xl_heap_newpage *xlrec = (xl_heap_newpage *) XLogRecGetData(record);
      Buffer            buffer;
      Page        page;

      /*
       * Note: the NEWPAGE log record is used for both heaps and indexes, so do
       * not do anything that assumes we are touching a heap.
       */
      buffer = XLogReadBuffer(xlrec->node, xlrec->blkno, true);
      Assert(BufferIsValid(buffer));
      page = (Page) BufferGetPage(buffer);

      Assert(record->xl_len == SizeOfHeapNewpage + BLCKSZ);
      memcpy(page, (char *) xlrec + SizeOfHeapNewpage, BLCKSZ);

      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);
}

static void
heap_xlog_delete(XLogRecPtr lsn, XLogRecord *record)
{
      xl_heap_delete *xlrec = (xl_heap_delete *) XLogRecGetData(record);
      Buffer            buffer;
      Page        page;
      OffsetNumber offnum;
      ItemId            lp = NULL;
      HeapTupleHeader htup;
      BlockNumber blkno;

      blkno = ItemPointerGetBlockNumber(&(xlrec->target.tid));

      /*
       * The visibility map always needs to be updated, even if the heap page is
       * already up-to-date.
       */
      if (xlrec->all_visible_cleared)
      {
            Relation    reln = CreateFakeRelcacheEntry(xlrec->target.node);

            visibilitymap_clear(reln, blkno);
            FreeFakeRelcacheEntry(reln);
      }

      if (record->xl_info & XLR_BKP_BLOCK_1)
            return;

      buffer = XLogReadBuffer(xlrec->target.node, blkno, false);
      if (!BufferIsValid(buffer))
            return;
      page = (Page) BufferGetPage(buffer);

      if (XLByteLE(lsn, PageGetLSN(page)))            /* changes are applied */
      {
            UnlockReleaseBuffer(buffer);
            return;
      }

      offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
      if (PageGetMaxOffsetNumber(page) >= offnum)
            lp = PageGetItemId(page, offnum);

      if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
            elog(PANIC, "heap_delete_redo: invalid lp");

      htup = (HeapTupleHeader) PageGetItem(page, lp);

      htup->t_infomask &= ~(HEAP_XMAX_COMMITTED |
                                      HEAP_XMAX_INVALID |
                                      HEAP_XMAX_IS_MULTI |
                                      HEAP_IS_LOCKED |
                                      HEAP_MOVED);
      HeapTupleHeaderClearHotUpdated(htup);
      HeapTupleHeaderSetXmax(htup, record->xl_xid);
      HeapTupleHeaderSetCmax(htup, FirstCommandId, false);

      /* Mark the page as a candidate for pruning */
      PageSetPrunable(page, record->xl_xid);

      if (xlrec->all_visible_cleared)
            PageClearAllVisible(page);

      /* Make sure there is no forward chain link in t_ctid */
      htup->t_ctid = xlrec->target.tid;
      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);
}

static void
heap_xlog_insert(XLogRecPtr lsn, XLogRecord *record)
{
      xl_heap_insert *xlrec = (xl_heap_insert *) XLogRecGetData(record);
      Buffer            buffer;
      Page        page;
      OffsetNumber offnum;
      struct
      {
            HeapTupleHeaderData hdr;
            char        data[MaxHeapTupleSize];
      }                 tbuf;
      HeapTupleHeader htup;
      xl_heap_header xlhdr;
      uint32            newlen;
      Size        freespace;
      BlockNumber blkno;

      blkno = ItemPointerGetBlockNumber(&(xlrec->target.tid));

      /*
       * The visibility map always needs to be updated, even if the heap page is
       * already up-to-date.
       */
      if (xlrec->all_visible_cleared)
      {
            Relation    reln = CreateFakeRelcacheEntry(xlrec->target.node);

            visibilitymap_clear(reln, blkno);
            FreeFakeRelcacheEntry(reln);
      }

      if (record->xl_info & XLR_BKP_BLOCK_1)
            return;

      if (record->xl_info & XLOG_HEAP_INIT_PAGE)
      {
            buffer = XLogReadBuffer(xlrec->target.node, blkno, true);
            Assert(BufferIsValid(buffer));
            page = (Page) BufferGetPage(buffer);

            PageInit(page, BufferGetPageSize(buffer), 0);
      }
      else
      {
            buffer = XLogReadBuffer(xlrec->target.node, blkno, false);
            if (!BufferIsValid(buffer))
                  return;
            page = (Page) BufferGetPage(buffer);

            if (XLByteLE(lsn, PageGetLSN(page)))      /* changes are applied */
            {
                  UnlockReleaseBuffer(buffer);
                  return;
            }
      }

      offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
      if (PageGetMaxOffsetNumber(page) + 1 < offnum)
            elog(PANIC, "heap_insert_redo: invalid max offset number");

      newlen = record->xl_len - SizeOfHeapInsert - SizeOfHeapHeader;
      Assert(newlen <= MaxHeapTupleSize);
      memcpy((char *) &xlhdr,
               (char *) xlrec + SizeOfHeapInsert,
               SizeOfHeapHeader);
      htup = &tbuf.hdr;
      MemSet((char *) htup, 0, sizeof(HeapTupleHeaderData));
      /* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
      memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
               (char *) xlrec + SizeOfHeapInsert + SizeOfHeapHeader,
               newlen);
      newlen += offsetof(HeapTupleHeaderData, t_bits);
      htup->t_infomask2 = xlhdr.t_infomask2;
      htup->t_infomask = xlhdr.t_infomask;
      htup->t_hoff = xlhdr.t_hoff;
      HeapTupleHeaderSetXmin(htup, record->xl_xid);
      HeapTupleHeaderSetCmin(htup, FirstCommandId);
      htup->t_ctid = xlrec->target.tid;

      offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
      if (offnum == InvalidOffsetNumber)
            elog(PANIC, "heap_insert_redo: failed to add tuple");

      freespace = PageGetHeapFreeSpace(page);         /* needed to update FSM below */

      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);

      if (xlrec->all_visible_cleared)
            PageClearAllVisible(page);

      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);

      /*
       * If the page is running low on free space, update the FSM as well.
       * Arbitrarily, our definition of "low" is less than 20%. We can't do much
       * better than that without knowing the fill-factor for the table.
       *
       * XXX: We don't get here if the page was restored from full page image.
       * We don't bother to update the FSM in that case, it doesn't need to be
       * totally accurate anyway.
       */
      if (freespace < BLCKSZ / 5)
            XLogRecordPageWithFreeSpace(xlrec->target.node, blkno, freespace);
}

/*
 * Handles UPDATE, HOT_UPDATE & MOVE
 */
static void
heap_xlog_update(XLogRecPtr lsn, XLogRecord *record, bool move, bool hot_update)
{
      xl_heap_update *xlrec = (xl_heap_update *) XLogRecGetData(record);
      Buffer            buffer;
      bool        samepage = (ItemPointerGetBlockNumber(&(xlrec->newtid)) ==
                                          ItemPointerGetBlockNumber(&(xlrec->target.tid)));
      Page        page;
      OffsetNumber offnum;
      ItemId            lp = NULL;
      HeapTupleHeader htup;
      struct
      {
            HeapTupleHeaderData hdr;
            char        data[MaxHeapTupleSize];
      }                 tbuf;
      xl_heap_header xlhdr;
      int               hsize;
      uint32            newlen;
      Size        freespace;

      /*
       * The visibility map always needs to be updated, even if the heap page is
       * already up-to-date.
       */
      if (xlrec->all_visible_cleared)
      {
            Relation    reln = CreateFakeRelcacheEntry(xlrec->target.node);

            visibilitymap_clear(reln,
                                          ItemPointerGetBlockNumber(&xlrec->target.tid));
            FreeFakeRelcacheEntry(reln);
      }

      if (record->xl_info & XLR_BKP_BLOCK_1)
      {
            if (samepage)
                  return;                       /* backup block covered both changes */
            goto newt;
      }

      /* Deal with old tuple version */

      buffer = XLogReadBuffer(xlrec->target.node,
                                          ItemPointerGetBlockNumber(&(xlrec->target.tid)),
                                          false);
      if (!BufferIsValid(buffer))
            goto newt;
      page = (Page) BufferGetPage(buffer);

      if (XLByteLE(lsn, PageGetLSN(page)))            /* changes are applied */
      {
            UnlockReleaseBuffer(buffer);
            if (samepage)
                  return;
            goto newt;
      }

      offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
      if (PageGetMaxOffsetNumber(page) >= offnum)
            lp = PageGetItemId(page, offnum);

      if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
            elog(PANIC, "heap_update_redo: invalid lp");

      htup = (HeapTupleHeader) PageGetItem(page, lp);

      if (move)
      {
            htup->t_infomask &= ~(HEAP_XMIN_COMMITTED |
                                            HEAP_XMIN_INVALID |
                                            HEAP_MOVED_IN);
            htup->t_infomask |= HEAP_MOVED_OFF;
            HeapTupleHeaderClearHotUpdated(htup);
            HeapTupleHeaderSetXvac(htup, record->xl_xid);
            /* Make sure there is no forward chain link in t_ctid */
            htup->t_ctid = xlrec->target.tid;
      }
      else
      {
            htup->t_infomask &= ~(HEAP_XMAX_COMMITTED |
                                            HEAP_XMAX_INVALID |
                                            HEAP_XMAX_IS_MULTI |
                                            HEAP_IS_LOCKED |
                                            HEAP_MOVED);
            if (hot_update)
                  HeapTupleHeaderSetHotUpdated(htup);
            else
                  HeapTupleHeaderClearHotUpdated(htup);
            HeapTupleHeaderSetXmax(htup, record->xl_xid);
            HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
            /* Set forward chain link in t_ctid */
            htup->t_ctid = xlrec->newtid;
      }

      /* Mark the page as a candidate for pruning */
      PageSetPrunable(page, record->xl_xid);

      if (xlrec->all_visible_cleared)
            PageClearAllVisible(page);

      /*
       * this test is ugly, but necessary to avoid thinking that insert change
       * is already applied
       */
      if (samepage)
            goto newsame;
      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);

      /* Deal with new tuple */

newt:;

      /*
       * The visibility map always needs to be updated, even if the heap page is
       * already up-to-date.
       */
      if (xlrec->new_all_visible_cleared)
      {
            Relation    reln = CreateFakeRelcacheEntry(xlrec->target.node);

            visibilitymap_clear(reln, ItemPointerGetBlockNumber(&xlrec->newtid));
            FreeFakeRelcacheEntry(reln);
      }

      if (record->xl_info & XLR_BKP_BLOCK_2)
            return;

      if (record->xl_info & XLOG_HEAP_INIT_PAGE)
      {
            buffer = XLogReadBuffer(xlrec->target.node,
                                                ItemPointerGetBlockNumber(&(xlrec->newtid)),
                                                true);
            Assert(BufferIsValid(buffer));
            page = (Page) BufferGetPage(buffer);

            PageInit(page, BufferGetPageSize(buffer), 0);
      }
      else
      {
            buffer = XLogReadBuffer(xlrec->target.node,
                                                ItemPointerGetBlockNumber(&(xlrec->newtid)),
                                                false);
            if (!BufferIsValid(buffer))
                  return;
            page = (Page) BufferGetPage(buffer);

            if (XLByteLE(lsn, PageGetLSN(page)))      /* changes are applied */
            {
                  UnlockReleaseBuffer(buffer);
                  return;
            }
      }

newsame:;

      offnum = ItemPointerGetOffsetNumber(&(xlrec->newtid));
      if (PageGetMaxOffsetNumber(page) + 1 < offnum)
            elog(PANIC, "heap_update_redo: invalid max offset number");

      hsize = SizeOfHeapUpdate + SizeOfHeapHeader;
      if (move)
            hsize += (2 * sizeof(TransactionId));

      newlen = record->xl_len - hsize;
      Assert(newlen <= MaxHeapTupleSize);
      memcpy((char *) &xlhdr,
               (char *) xlrec + SizeOfHeapUpdate,
               SizeOfHeapHeader);
      htup = &tbuf.hdr;
      MemSet((char *) htup, 0, sizeof(HeapTupleHeaderData));
      /* PG73FORMAT: get bitmap [+ padding] [+ oid] + data */
      memcpy((char *) htup + offsetof(HeapTupleHeaderData, t_bits),
               (char *) xlrec + hsize,
               newlen);
      newlen += offsetof(HeapTupleHeaderData, t_bits);
      htup->t_infomask2 = xlhdr.t_infomask2;
      htup->t_infomask = xlhdr.t_infomask;
      htup->t_hoff = xlhdr.t_hoff;

      if (move)
      {
            TransactionId xid[2];   /* xmax, xmin */

            memcpy((char *) xid,
                     (char *) xlrec + SizeOfHeapUpdate + SizeOfHeapHeader,
                     2 * sizeof(TransactionId));
            HeapTupleHeaderSetXmin(htup, xid[1]);
            HeapTupleHeaderSetXmax(htup, xid[0]);
            HeapTupleHeaderSetXvac(htup, record->xl_xid);
      }
      else
      {
            HeapTupleHeaderSetXmin(htup, record->xl_xid);
            HeapTupleHeaderSetCmin(htup, FirstCommandId);
      }
      /* Make sure there is no forward chain link in t_ctid */
      htup->t_ctid = xlrec->newtid;

      offnum = PageAddItem(page, (Item) htup, newlen, offnum, true, true);
      if (offnum == InvalidOffsetNumber)
            elog(PANIC, "heap_update_redo: failed to add tuple");

      if (xlrec->new_all_visible_cleared)
            PageClearAllVisible(page);

      freespace = PageGetHeapFreeSpace(page);         /* needed to update FSM below */

      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);

      /*
       * If the page is running low on free space, update the FSM as well.
       * Arbitrarily, our definition of "low" is less than 20%. We can't do much
       * better than that without knowing the fill-factor for the table.
       *
       * However, don't update the FSM on HOT updates, because after crash
       * recovery, either the old or the new tuple will certainly be dead and
       * prunable. After pruning, the page will have roughly as much free space
       * as it did before the update, assuming the new tuple is about the same
       * size as the old one.
       *
       * XXX: We don't get here if the page was restored from full page image.
       * We don't bother to update the FSM in that case, it doesn't need to be
       * totally accurate anyway.
       */
      if (!hot_update && freespace < BLCKSZ / 5)
            XLogRecordPageWithFreeSpace(xlrec->target.node,
                               ItemPointerGetBlockNumber(&(xlrec->newtid)), freespace);
}

static void
heap_xlog_lock(XLogRecPtr lsn, XLogRecord *record)
{
      xl_heap_lock *xlrec = (xl_heap_lock *) XLogRecGetData(record);
      Buffer            buffer;
      Page        page;
      OffsetNumber offnum;
      ItemId            lp = NULL;
      HeapTupleHeader htup;

      if (record->xl_info & XLR_BKP_BLOCK_1)
            return;

      buffer = XLogReadBuffer(xlrec->target.node,
                                          ItemPointerGetBlockNumber(&(xlrec->target.tid)),
                                          false);
      if (!BufferIsValid(buffer))
            return;
      page = (Page) BufferGetPage(buffer);

      if (XLByteLE(lsn, PageGetLSN(page)))            /* changes are applied */
      {
            UnlockReleaseBuffer(buffer);
            return;
      }

      offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
      if (PageGetMaxOffsetNumber(page) >= offnum)
            lp = PageGetItemId(page, offnum);

      if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
            elog(PANIC, "heap_lock_redo: invalid lp");

      htup = (HeapTupleHeader) PageGetItem(page, lp);

      htup->t_infomask &= ~(HEAP_XMAX_COMMITTED |
                                      HEAP_XMAX_INVALID |
                                      HEAP_XMAX_IS_MULTI |
                                      HEAP_IS_LOCKED |
                                      HEAP_MOVED);
      if (xlrec->xid_is_mxact)
            htup->t_infomask |= HEAP_XMAX_IS_MULTI;
      if (xlrec->shared_lock)
            htup->t_infomask |= HEAP_XMAX_SHARED_LOCK;
      else
            htup->t_infomask |= HEAP_XMAX_EXCL_LOCK;
      HeapTupleHeaderClearHotUpdated(htup);
      HeapTupleHeaderSetXmax(htup, xlrec->locking_xid);
      HeapTupleHeaderSetCmax(htup, FirstCommandId, false);
      /* Make sure there is no forward chain link in t_ctid */
      htup->t_ctid = xlrec->target.tid;
      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);
}

static void
heap_xlog_inplace(XLogRecPtr lsn, XLogRecord *record)
{
      xl_heap_inplace *xlrec = (xl_heap_inplace *) XLogRecGetData(record);
      Buffer            buffer;
      Page        page;
      OffsetNumber offnum;
      ItemId            lp = NULL;
      HeapTupleHeader htup;
      uint32            oldlen;
      uint32            newlen;

      if (record->xl_info & XLR_BKP_BLOCK_1)
            return;

      buffer = XLogReadBuffer(xlrec->target.node,
                                          ItemPointerGetBlockNumber(&(xlrec->target.tid)),
                                          false);
      if (!BufferIsValid(buffer))
            return;
      page = (Page) BufferGetPage(buffer);

      if (XLByteLE(lsn, PageGetLSN(page)))            /* changes are applied */
      {
            UnlockReleaseBuffer(buffer);
            return;
      }

      offnum = ItemPointerGetOffsetNumber(&(xlrec->target.tid));
      if (PageGetMaxOffsetNumber(page) >= offnum)
            lp = PageGetItemId(page, offnum);

      if (PageGetMaxOffsetNumber(page) < offnum || !ItemIdIsNormal(lp))
            elog(PANIC, "heap_inplace_redo: invalid lp");

      htup = (HeapTupleHeader) PageGetItem(page, lp);

      oldlen = ItemIdGetLength(lp) - htup->t_hoff;
      newlen = record->xl_len - SizeOfHeapInplace;
      if (oldlen != newlen)
            elog(PANIC, "heap_inplace_redo: wrong tuple length");

      memcpy((char *) htup + htup->t_hoff,
               (char *) xlrec + SizeOfHeapInplace,
               newlen);

      PageSetLSN(page, lsn);
      PageSetTLI(page, ThisTimeLineID);
      MarkBufferDirty(buffer);
      UnlockReleaseBuffer(buffer);
}

void
heap_redo(XLogRecPtr lsn, XLogRecord *record)
{
      uint8       info = record->xl_info & ~XLR_INFO_MASK;

      RestoreBkpBlocks(lsn, record, false);

      switch (info & XLOG_HEAP_OPMASK)
      {
            case XLOG_HEAP_INSERT:
                  heap_xlog_insert(lsn, record);
                  break;
            case XLOG_HEAP_DELETE:
                  heap_xlog_delete(lsn, record);
                  break;
            case XLOG_HEAP_UPDATE:
                  heap_xlog_update(lsn, record, false, false);
                  break;
            case XLOG_HEAP_MOVE:
                  heap_xlog_update(lsn, record, true, false);
                  break;
            case XLOG_HEAP_HOT_UPDATE:
                  heap_xlog_update(lsn, record, false, true);
                  break;
            case XLOG_HEAP_NEWPAGE:
                  heap_xlog_newpage(lsn, record);
                  break;
            case XLOG_HEAP_LOCK:
                  heap_xlog_lock(lsn, record);
                  break;
            case XLOG_HEAP_INPLACE:
                  heap_xlog_inplace(lsn, record);
                  break;
            default:
                  elog(PANIC, "heap_redo: unknown op code %u", info);
      }
}

void
heap2_redo(XLogRecPtr lsn, XLogRecord *record)
{
      uint8       info = record->xl_info & ~XLR_INFO_MASK;

      switch (info & XLOG_HEAP_OPMASK)
      {
            case XLOG_HEAP2_FREEZE:
                  RestoreBkpBlocks(lsn, record, false);
                  heap_xlog_freeze(lsn, record);
                  break;
            case XLOG_HEAP2_CLEAN:
                  RestoreBkpBlocks(lsn, record, true);
                  heap_xlog_clean(lsn, record, false);
                  break;
            case XLOG_HEAP2_CLEAN_MOVE:
                  RestoreBkpBlocks(lsn, record, true);
                  heap_xlog_clean(lsn, record, true);
                  break;
            default:
                  elog(PANIC, "heap2_redo: unknown op code %u", info);
      }
}

static void
out_target(StringInfo buf, xl_heaptid *target)
{
      appendStringInfo(buf, "rel %u/%u/%u; tid %u/%u",
                   target->node.spcNode, target->node.dbNode, target->node.relNode,
                               ItemPointerGetBlockNumber(&(target->tid)),
                               ItemPointerGetOffsetNumber(&(target->tid)));
}

void
heap_desc(StringInfo buf, uint8 xl_info, char *rec)
{
      uint8       info = xl_info & ~XLR_INFO_MASK;

      info &= XLOG_HEAP_OPMASK;
      if (info == XLOG_HEAP_INSERT)
      {
            xl_heap_insert *xlrec = (xl_heap_insert *) rec;

            if (xl_info & XLOG_HEAP_INIT_PAGE)
                  appendStringInfo(buf, "insert(init): ");
            else
                  appendStringInfo(buf, "insert: ");
            out_target(buf, &(xlrec->target));
      }
      else if (info == XLOG_HEAP_DELETE)
      {
            xl_heap_delete *xlrec = (xl_heap_delete *) rec;

            appendStringInfo(buf, "delete: ");
            out_target(buf, &(xlrec->target));
      }
      else if (info == XLOG_HEAP_UPDATE)
      {
            xl_heap_update *xlrec = (xl_heap_update *) rec;

            if (xl_info & XLOG_HEAP_INIT_PAGE)
                  appendStringInfo(buf, "update(init): ");
            else
                  appendStringInfo(buf, "update: ");
            out_target(buf, &(xlrec->target));
            appendStringInfo(buf, "; new %u/%u",
                                     ItemPointerGetBlockNumber(&(xlrec->newtid)),
                                     ItemPointerGetOffsetNumber(&(xlrec->newtid)));
      }
      else if (info == XLOG_HEAP_MOVE)
      {
            xl_heap_update *xlrec = (xl_heap_update *) rec;

            if (xl_info & XLOG_HEAP_INIT_PAGE)
                  appendStringInfo(buf, "move(init): ");
            else
                  appendStringInfo(buf, "move: ");
            out_target(buf, &(xlrec->target));
            appendStringInfo(buf, "; new %u/%u",
                                     ItemPointerGetBlockNumber(&(xlrec->newtid)),
                                     ItemPointerGetOffsetNumber(&(xlrec->newtid)));
      }
      else if (info == XLOG_HEAP_HOT_UPDATE)
      {
            xl_heap_update *xlrec = (xl_heap_update *) rec;

            if (xl_info & XLOG_HEAP_INIT_PAGE)        /* can this case happen? */
                  appendStringInfo(buf, "hot_update(init): ");
            else
                  appendStringInfo(buf, "hot_update: ");
            out_target(buf, &(xlrec->target));
            appendStringInfo(buf, "; new %u/%u",
                                     ItemPointerGetBlockNumber(&(xlrec->newtid)),
                                     ItemPointerGetOffsetNumber(&(xlrec->newtid)));
      }
      else if (info == XLOG_HEAP_NEWPAGE)
      {
            xl_heap_newpage *xlrec = (xl_heap_newpage *) rec;

            appendStringInfo(buf, "newpage: rel %u/%u/%u; blk %u",
                                     xlrec->node.spcNode, xlrec->node.dbNode,
                                     xlrec->node.relNode, xlrec->blkno);
      }
      else if (info == XLOG_HEAP_LOCK)
      {
            xl_heap_lock *xlrec = (xl_heap_lock *) rec;

            if (xlrec->shared_lock)
                  appendStringInfo(buf, "shared_lock: ");
            else
                  appendStringInfo(buf, "exclusive_lock: ");
            if (xlrec->xid_is_mxact)
                  appendStringInfo(buf, "mxid ");
            else
                  appendStringInfo(buf, "xid ");
            appendStringInfo(buf, "%u ", xlrec->locking_xid);
            out_target(buf, &(xlrec->target));
      }
      else if (info == XLOG_HEAP_INPLACE)
      {
            xl_heap_inplace *xlrec = (xl_heap_inplace *) rec;

            appendStringInfo(buf, "inplace: ");
            out_target(buf, &(xlrec->target));
      }
      else
            appendStringInfo(buf, "UNKNOWN");
}

void
heap2_desc(StringInfo buf, uint8 xl_info, char *rec)
{
      uint8       info = xl_info & ~XLR_INFO_MASK;

      info &= XLOG_HEAP_OPMASK;
      if (info == XLOG_HEAP2_FREEZE)
      {
            xl_heap_freeze *xlrec = (xl_heap_freeze *) rec;

            appendStringInfo(buf, "freeze: rel %u/%u/%u; blk %u; cutoff %u",
                                     xlrec->node.spcNode, xlrec->node.dbNode,
                                     xlrec->node.relNode, xlrec->block,
                                     xlrec->cutoff_xid);
      }
      else if (info == XLOG_HEAP2_CLEAN)
      {
            xl_heap_clean *xlrec = (xl_heap_clean *) rec;

            appendStringInfo(buf, "clean: rel %u/%u/%u; blk %u",
                                     xlrec->node.spcNode, xlrec->node.dbNode,
                                     xlrec->node.relNode, xlrec->block);
      }
      else if (info == XLOG_HEAP2_CLEAN_MOVE)
      {
            xl_heap_clean *xlrec = (xl_heap_clean *) rec;

            appendStringInfo(buf, "clean_move: rel %u/%u/%u; blk %u",
                                     xlrec->node.spcNode, xlrec->node.dbNode,
                                     xlrec->node.relNode, xlrec->block);
      }
      else
            appendStringInfo(buf, "UNKNOWN");
}

/*
 *    heap_sync         - sync a heap, for use when no WAL has been written
 *
 * This forces the heap contents (including TOAST heap if any) down to disk.
 * If we skipped using WAL, and it's not a temp relation, we must force the
 * relation down to disk before it's safe to commit the transaction.  This
 * requires writing out any dirty buffers and then doing a forced fsync.
 *
 * Indexes are not touched.  (Currently, index operations associated with
 * the commands that use this are WAL-logged and so do not need fsync.
 * That behavior might change someday, but in any case it's likely that
 * any fsync decisions required would be per-index and hence not appropriate
 * to be done here.)
 */
void
heap_sync(Relation rel)
{
      /* temp tables never need fsync */
      if (rel->rd_istemp)
            return;

      /* main heap */
      FlushRelationBuffers(rel);
      /* FlushRelationBuffers will have opened rd_smgr */
      smgrimmedsync(rel->rd_smgr, MAIN_FORKNUM);

      /* FSM is not critical, don't bother syncing it */

      /* toast heap, if any */
      if (OidIsValid(rel->rd_rel->reltoastrelid))
      {
            Relation    toastrel;

            toastrel = heap_open(rel->rd_rel->reltoastrelid, AccessShareLock);
            FlushRelationBuffers(toastrel);
            smgrimmedsync(toastrel->rd_smgr, MAIN_FORKNUM);
            heap_close(toastrel, AccessShareLock);
      }
}

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